1d8+DB

Hmmm. Perhaps you're being overly ambitious? I would collapse the 'Ages' into three myself: pre-industrial (neo-lithic up to Renaissance), industrial (Steam up to Atom Age), and information age (beginning of internet age up to trans-human/cyberpunk era). I don't think the distinctions are otherwise, game-wise, that significant.

I hear that there's a 'director's cut' that you can only find in Europe! 😉

I suspect there's a quite a bit of importance attached to who specifically you're fighting. Tribal Enemies, enemies from within your home culture (in the default setting this would be Sartarites). Out of Tribe enemies, enemies from foreign cultures (in the default setting this would most likely be Lunars). And 'Enemies of All'; bandits, oath-breakers, and the Chaos-tainted. In the latter it would be straight up 'Murder Hobo' time: kill them, and if they have anything that won't give me a disease or poison my soul with Chaos, take it. Out of Tribe Enemies would involve personal ransoms, but not necessarily equipment; though much captured equipment might end as a temple offering (no self-respecting Thane is going to want to be seen wearing a khopesh!). For Tribal Enemies there's probably a lengthy period of negotiation before the combat; how long will we fight, what are the boundaries of the battle-field, who are the healers. Part of this negotiation might involve staking 'prizes'. 'If we lose you get two mounts of your choice, and their tack. And if you lose we get Tarrek's bronze greaves and vambraces, and the 'Ever Plentiful Jug'. In some cases the 'prize' might be in the form of promises or favors, or even reputation bonuses: 'Tell the next three people you meet how we defeated you this day.'

So looking at the combat example on page 115, on round 2, when the ghoul enters melee combat with Harvey; Harvey get's a bonus die for Point Blank range (which he then looses because he's firing off multiple rounds), there's no mention of the 'Firing Into Melee' modifier. There's a difference between 'Firing INTO Melee' and 'Firing WHILE IN Melee'. In the latter case you only use the Point Blank range modifier. If you want to be really simulationist you might require a successful Fighting Maneuver if an individual with a long-arm (rifle) is engaged in Melee, as the shooter has to make sure the gun-barrel is not batted aside or pushed to the side. It's your game, and can play as you wish; but I think the intent of the designers is clear-- if you're using a fire-arm in melee, you get the Point Blank modifier (unless of course you are shooting someone beyond your immediate combatant).

Not in a position where I can check my rulebook: but I thought the 'Firing into Melee' rule was for situations where character A fires at character B, who is is in Melee combat with character C. The Penalty die is because A is trying to avoid hitting C. So what matters here is how close B is to C. So if B and C are in Melee combat, and A is within Point Blank range (1/5 Dex) of both combatants, I would probably rule that that the Point Blank Bonus and the Firing Into Melee Penalty cancel each other out.

So one thing you could do are Gun Cherries (an idea used in Night's Black Agents from Pelgrane Press): minor mechanical effects that the Play Characters can apply to their weapons; as a heavy pistol in the hands of a mook is just a heavy pistol; but a heavy pistol in the hands of a Player Character is a 'Kruge Arms S-2000 Special Model.' Let the Players create your weapon catalog. I would consider asking for either a spend of temporary POW to active the Gun Cherry, or require a special success on the fire-arms roll; to reflect the specialized training that the Player Character has to draw on to get the most of the weapon.

A Shoggoth? I would say no; that's deep Mythos mojo there. A cryo-sleep chamber? Definitely.

No, as the OP noted, it appears to be a real, though rare cartridge: it looks like it had two major iterations, the 1877 Colt, and the .41 Remington Magnum (from 1963).

Yeah, the 'Powers' are the way to go: I was thinking of Teleportion instead of Super Movement, but that works. I wonder about using Passions to manage the Pact, Loyalty to the Bureau vs. Demonic Corruption as oppositional drives. Also, depending on how dark you want the tone, you might want to incorporate Sanity Rules, as being a conduit for demonic powers might be somewhat traumatizing.

I wouldn't discount the 'psychic influence' of the Mythos. Just finished F. Paul Wilson's 'Conspiracies', the 3rd book in his 'Repairman Jack' series, which is Mythos 'adjacent'; and there's definitely a kind of mental miasma in places where the 'Otherness' has bled through (the hotel hosting the SESOUP conference and the basement of Melanie's house). Obviously in no way canonical, but it suggests how entities of Mythos might just radiate 'wrongness' in a non-visual way.

Personally, if I brought this to the table I would most likely use the combat mechanics/equipment list from Openquest, the Passions/Factions from RD/BRP/Pendragon/Mythras, and the Magic/Sanity rules from CoC/Dark Ages.

I would see no reason why not. The main change would be the absence of gunpowder weapons (save for a rare 'handgonne' or 'bombard'). The Close Combat weapons list would be largely unchanged (though you might want to lose the rapiers and side-swords). You might have to fudge the armor definitions a bit; substituting mail for buff-coats for instance. Pretty much the main 'mechanical' difference between a renaissance period game and a late medieval period game is going to be the growing prevalence of gun-powder weapons. Everything else, the social and cultural changes, the transition from feudal states to absolute monarchies for example, are just going to be matters of roleplaying 'fluff.'

How many monsters should a TTFRPG have? I like 'Bestiaries': I have vols. 1 thru 5 for PF 1e. They're lots of fun and I get a lot of inspiration from them, but I don't think having hundreds, or thousands, of monsters is necessary for a great campaign. How much really comes down to just a few numbers in the stat-block? There is the old bit of 'DM' advice about 'The Bear'. X Hit points, X Armor Points, a Bite and a Claw attack doing X damage. Change up the description It's an a savage denizen of the deep woods. Its an emaciated, shambling undead. It's a scaled, reptilian survivor of a lost world. Its a Bite and Claw attack. Multiple monsters from the same stat-block. The same monster can yield up a wildly different 'feel' depending on the encounter context. Run into a party of broo/orcs in the wilderness. Fight them before the gates of a beleaguered village, or face them in their subterranean lair. Same monsters, different encounters requiring different Player Character tactics. In a setting where 'Nightvision' isn't ubiquitous environmental conditions can radically change an encounter. Can you even see what's creeping beyond the circle of torch-light.? So the terrain and other conditions can and should bring variety to encounters. Monsters can be categorized by their combat roles: mooks, 'snipers' with ranged attacks, perhaps magical ones; creatures which do brutal damage; creatures which can only be harmed by select attacks; and creatures which can target character abilities and equipment. Monsters in different combinations of these roles can lead to a lot of varied play. A troll with a pack of zombie servitors at night in a humid swamp. A giant and his wolves in an alpine pass while a blizzard rages. An encounter with a monster should be more than just putting a miniature on the table. Finally, for the 'grim-dark' style I prefer; having ten different types of humanoids for each terrain type is just silly. I think generally my games probably break down as follows: 40% Human. Peasants, traders, nobles and their entourages, bandits, raiders, and cultists. 25% Non-humans. What-ever intelligent non-humans are present in the setting. 10% Animals. Could include mega-fauna, dinosaurs, or 'giant' variants. 15% Mythic/Magical. Your dragons, basilisks, giant's etc. 8% Sorcery-spawned. Undead, demons, constructs, and the like. 1%. Unique. Legendary creatures, fallen gods, vortices of sentient magic, planar travelers.

So there's an indie game of 'colloborative' story-telling and narrative role-playing called 'Microscope'. You can play and create epic arcs ('The Five Thousand Reign of the God Emperor'), zeroing in on specific periods ('The Trade Wars') and key figures ('Lady Rhaya Mhazil of the Ardara Counting House'). I thought I would like to try it to create a back-ground/history for use in a more conventional TTRPG. You could also use it to to create a narrative frame-work that you could then slot your PD/BRP 'mini-campaigns' into for a generational/supra-historical game.

So its not an OSR, but '13th Age' might be a possibility; it's pretty much 3-4e D&D, but very much pared down and simplified. Pretty much all the familiar classes and 'peoples' are present. Some brief notes on some OSR games that I own. 'Lamentations of the Flame Princess': Pretty much a straight 'white-box' clone. Stuff written for it pretty much slews to the horror side of play, so might not be entirely appropriate for some younger players. 'Knave': Seven pages of rules only. Very bare-bones. There's a 2nd edition in the pipe-line. Its only a few dollars at DrivethruRPG. 'Dungeon World': This introduced player-sided mechanics, which has been widely embraced in the OSR world; only the players ever roll the dice. There's a 20-sided mechanic: 15+ you succeed, do damage, etc. 9-14, you succeed, but the DM gets a 'Move'; they can introduce a complication (more Orcs rush into the melee), 13 or less and you fail and the DM gets their move. 'Mork Borg': This made a quite a splash when it came out, largely for its gonzo art-style and lay-out. Another game with player-sided mechanics. Rules are pretty much reduced to a few a paragraphs. It's grim-dark turned up to '11'. It's goblins are terrifying (fight one, and if it survives the combat, you will become a goblin). 'Warlock' and 'Warpstar': The first is fantasy while the second is space-opera. Heavily influenced by the Warhammer line, with 'Careers' and 'Wound tables'. Besides your skills you only have two characteristics: 'Luck' and 'Stamina' (hit-points). And to finish I'll name-drop three that I don't have, but appear to have large followings: 'Dungeon Crawl Classics'. 'Index Card RPG.' 'Old School Essentials.'