Most retail games on the PSN store seem to be a solid 3GB. So the 32GB would be your best bet if you want to store 8 games at a time.
Before you can get games, you need to BUY them. So it might be worth getting $100 worth of PSN money for $80.
Nope - no need for the PSN money except for the occasional purchase (and I think I have a couple of $20 cards in a drawer from some long-ago Kmart deal). I expect to get plenty of PSN stuff from PS+. I actually went with the 8GB bundle because I thought I wouldn't be getting a lot of downloadable games. PS+ threw a wrench into those plans
I think I'm just going to stick with the 8GB and only put on there what I need when I need it. With PS+ cloud saving I can back up any saves before I delete the games. I don't expect to play the Vita all that much and won't be taking it anywhere so I don't need to have everything on the card at once - can always redownload what I need. In fact, I think the first thing I'm going to do is delete Wipeout and Gravity Rush and get Uncharted on there since I want to play that first.
Anyway, off topic... I guess I should look for my $25 small business credit. I bought a $25 gift card at a local movie theater - so, yeah, a free movie with a couple of my kids!