Every group is going to become familiar with whatever adjectives they use to describe their initiative plans. No specific numbers is the rule and even with familiarity, my group occasionally guesses each other's wrong.

The campaign doesn't have any ticking clocks. There are some choices you can make along the way that lock you out of certain scenarios.

IMO, the classes I've seen so far are flexible enough that you could make any pairing work. Some pairings are obviously better/worse than others, but with planning, I don't think any are so broken that you can't win. You can always adjust the difficulty or just start a new character if you don't like your current part comp.