Whenever I try to do a 5-man, inevitably one of them ends up in the bullpen most of the time. It's not necessarily bad, you just have to expect it to happen and plan accordingly. Usually I have 4 in the rotation and one as a setup, and when the first rotation guy starts not bouncing back to 100%, I swap him and the setup guy.
It varies by cap, but usually you only need 950-1050 innings in your rotation. 1000 innings is ~15,000 pitches, which is 92.5 per game. You can do more, but you run the risk of not using them if your pitchers get pulled early. You can do less, but you need a really deep bullpen which tends to wear out.