I'll be slightly different here... I think it's a good thing to start off straight away with a RWD car, so that driving RWD cars becomes an instinct. The longer you drive one, the better. A daily driver, even better in my opinion.
I would suggest get an S15 Spec-S, whilst still saving up for the Spec-R, enjoy the fun of a light RWD car, and when you have enough money saved up for the differnce in price of a Spec-R, sell the Spec-S and get the Spec-R...
Seriously, I have owned all sorts of crazy cars (some with mad power) in the past 10 or so years, and the Spec-S was
awesome to drive daily. Trouble free, reliable, tail-happy in a really safe way and quite quick. When I say "safe" I mean the likelihood of rescuing a turn gone horribly wrong is easier; by no means is it a crappy car (and I'm not necessarily a Nissan fan and am blinded; I've owned all types and brands of cars).
Horsepower.. don't believe the hype, and you will remember me someday; all those big numbers.. pointless if the drive isn't fun or really frustrating if you have to keep fixing parts that are breaking. Doesn't meant don't do it, but do take your time and enjoy the car when you get it
Good luck!