Absent demon weapons or superhuman strength (either of which should disqualify an adversary from characterization as "lesser"), weapon breaking is only likely if they're rolling critical attacks, which was as said is the one thing highly skilled fighters should fear. Having your sword broken by a succession of critical parries is possible, but unlikely, because your opponent is going to roll about as many critical attacks as critical parries, and the former will, unless you incapacitate him first, most likely have put you and/or your sword out of commission before the later becomes an issue.
And that's assuming you're not using a shield.
Not really, in my experience. The rules, specifically how multiple parries work, are very lenient on characters with multiple opponents.
Well, sure, a high weapon skill doesn't help against getting shot. It doesn't help against rocks falling from the sky, or anything else that can't be parried, either. My comment was about close combat.