(Spoilers to follow)
To be honest, the campaign's introductory scenario is a remarkably solid start as is - there's minimal risk, but it's also notably weird and does a remarkably good job of driving home how big a deal things are (we ended up with a single character surviving from the performance into Act 2, and she was basically the driving force of the campaign).
Otherwise... a scenario that lets you introduce Estus is useful, or Grahame's brother (who's name escapes me) - I think having a personal tie and opinion of him will help give that first act a little more nuance.
I'd avoid anything dealing with Shub-Nigurath or the Tcho-Tcho, I suspect their chapters works best if the characters and players have as little knowledge of exactly what's going on as possible (or little enough that they're willing to work with them, instead of assuming antagonism). Something involving Chaugnar-Faugn wouldn't hurt - his presence in the campaign always felt a little bit tacked-on, and having the players be familiar enough with him for his appearance to merit a reaction would probably enhance that.
None of which is probably hugely useful, as I can't, off the top of my head, suggest any adventures that fit that criteria!
But good luck either way, I'm a big fan of Tatters - it's a remarkably well written campaign, and I'm more than happy to offer any advice I can from my playthrough
(...like, off the top of my head, be aware when wrapping up Act 1 that the players are entirely within their rights to assume that everyone of importance is now dead, and there's no need to investigate the beginning of Act 2. I think I wrote them an extra letter from Their Friend to prod them into action)