How many Q's are in GMAT Prep software?

They don't officially publish that information but we've estimated it to be in the 200 to 300 range. Also, the two "clean" tests you can take are drawn from separate databases of questions. Remember that those questions are at varying difficulty levels, so you wouldn't be "eligible" for all of them, one way or another. So do feel free to take the tests multiple times, but most people notice repeats the first time they re-take one.

If you only have a couple that you remember, it's no big deal. Just remember to do this: if you see a question you recognize, immediately glance at the clock. Make yourself sit there for the full 2 min (1.5 for SC) even if you literally remember the answer and can answer immediately. That way, at least, you won't give yourself an advantage on other questions later in the section because you didn't use all the time you would've on a new question.