Of what you listed I would purchase in the following order:
1. wetsuit
2. regulator
3. bag
4. BCD
5. computer
Wetsuit is the item that is most dependent on being a personal fit, and rental suits are kind of gross. If you want to splurge and by more gear I would go with regs next; however, rental regs (as well as BCs and computers) are totally fine for the type of diving you will be doing. My only piece of advice would be to thoroughly research here on scubaboard before buying and don't let a dive shop cheat you.
As far as a watch goes, I have a cheap timex. Doesn't matter if it is a "dive watch" or not, as long as it is pressure rated. I paid like $25 for it. If it breaks I'll just buy another...If you are looking at $250 watches you might as well just buy a computer (Hollis DG03, Mares puck, suunto zoop)
---------- Post added March 22nd, 2013 at 09:01 PM ----------
Yeah if you are only going to be diving once a year it probably makes more sense to just rent. I would still consider getting your own wetsuit however