As far as trems are concerned-
The stock Strat trem has an iffy record when it comes to staying in tune... it seems to vary from guitar to guitar, and just how much you ream on that bar. You don't neccesarily need a locking nut for it to stay in tune; a roller nut (or even a stock nut) will work just fine depending on the guitar. SO ANYWAY, the basic rule is that if you're going to be doing extream vibrato (divebombing, etc) you'll probably want a floyd rose style whammy bar with a locking nut. If you're just going to do some slight stuff for the most part shop around and find a Strat that stays in tune well with that sort of thing. And you will have to shop around, you can take any 5 strats with exactly the same set up, and they'll all behave differently when you use your tremlo.

The long and short of this really is that you should go to every guitar shop in your area, and play every guitar they have until you find THE STRAT (or Strat clone) for you. I bought my strat when I came in looking for a mic cable... I just turned around and there it was (I didn't see the other two Strats next to it for atleast half an hour after I had played it, put it back, and tried it again).
Well, good luck.