1) What ever you do, have a car PPI'd by a reputable shop that has no interest in the car that is being sold. Ideally you want to be there during the whole time.
2) Start reading the Pelican 911 board. It's one of the best Porsche related boards around.
http://forums.pelicanparts.com/forumdispla...=&forumid=83) Buy Bruce Anderson's 911 Porsche Handbook. It's a great resource for 914 owners too. It has a good rundown of all the various models, all the engines, transmissions, wheels, specs, etc. He also goes over common failure points for particular models.
4) Bruce always says to buy the newest, best 911 you can afford. There is a certain wisdom in that advice. You also got to know what you want. Do you want an older car that will present a lot of DIY projects or a no fuss, no mess 996 that you can drive every day with new car reliability?
I also like this site:
http://www.idee.demon.nl/ for a run down of all the models with a little history thrown in.
5) With a 911 figure on a higher yearly maintenance budget than with a 914/4. I'd say $1000-1500/year is in the ballpark depending on how much you farm out. With a 911, you might go for a few years needing just oil changes and then you need a clutch, transmission, or upper end on the engine which can run into the thousands of dollars. 911s are pretty reliable but that big repair bill needs to be anticipated and amortized over time.
6) DO NOT SKIP STEP 1!