Which E36's are worth modifying?

Ive recently decided of maybe getting a 3 series E36 i just have a few general questions.

Whats the difference say between 92-95 325i and a 96-97 323i i think they have the same engine so is there any difference.

Also if i cant afford a 325i i want to know is it worth modifying a 318i or 320i and is there a real big speed difference between a 325i and 320i.

I heard one of the first things 325i get modded with are performance chips. Approx how much are they and how much performace are gained

Thanks for anyones help, up until now i was always going to get a skyline and i decided id rather probaly have an beamer so i just need some info

You are right about the engine. While the BMW 325 was in the crossover stage to the 323 there were some cars that still had the 2.5 litre although it wore the 323 badge. If I were you I would shoot for atleast a 325. I really dont care for the 318. A dinan chip runs around $300, i dont know the exact price but i do know that at peak rpms with a cold air the chip can give you 20hp. Now the last part of your message kills me, you cant afford anything higher than a 318 but you can afford a skyline which will cost you about 80,000 including import. I think your just playing around

Nah im not playing around where you from, im from Australia. I can get a modified R33 for about $20 000AU but i cant find an E36 325i under $25 000AU. But there are just too many skylines now in australia so i wouldnt mind being different and getting a 325i