It all depends on what you want to do. Do you plan on modifying the car at all? ie. supercharger or engine work. If you plan on doing any engine modifications, I would highly recommend staying with an OBD1 engine which is pre-'95. 1996 model year was an OBDII engine which requires flashing the DMU for any engine upgrades. Much more difficult. If do not plan on modifying the car, then I agree with the upper thread, purchase as new as your money can afford.
The only difference between the 325i and 325is is the Sport package - which I highly recommend. Gives you stiffer springs and suspension pieces for spirited driving. Definately get a 5 speed manual - the auto's of that vintage was not very strong. I've gone through two auto trannys and am swapping for a 5 speed.
Other than that, BMW's engine's are very strong and should give you a couple hundred thousand miles of driving as long as you take care of them.
As far as websites, go to Bimmerforums.com which will provide a wealth of information concerning BMW's.