I won Fantasy Gym last year (man, I've been waiting to bring that up for MONTHS!).  It's hard to say how much difference it will end up making in any given year, but I'd suggest using all 150 picks, with at least 100 of those being returning gymnasts who competed regularly. Chances are, you can't think of 100 people matching that description off the top of your head, but that's where last season's numbers come in. Then you can use your remaining 25-50 spots for "unproven" gymnasts (i.e. freshmen and people coming back from injury) you're excited about.  Also, don't be afraid to take your gut feelings about gymnasts into consideration when you're ranking your list; it sure paid off for me. I  wouldn't exactly call Katherine Grable, Lindsey Cheek, and Kim Jacob, "dark horses" but I put them all in my top 10 over people like Joanna Sampson or Kytra Hunter. Those three all happened to have pretty great meets at Nationals (apart from Kim Jacob's beam issues) and I ended up winning the title. On a similar note, I put Maile'ana Kanewa and Kiera Brown in my top 20 just because I had a good feeling about both of them.  Kanewa ended up really blowing the post-season out of the water, and Brown turned out to be a godsend on bars and eventually beam. 

I agree that you don't want to end up with too many people from the same team, and if you do, you defintely want to watch how many people from the same school you're putting up on any given event. A few meets were cancelled last season because of inclement weather. If you have four or more gymnasts from the same team in one of your lineups, and that team is in a meet that gets cancelled, you're automatically counting a zero.