From the outside, the easiest way to tell between a 210 and 225 are the wing mirrors. 210s had a squarer mirror the same as the Mk IV Golf. 225s have a teardrop shaped mirror. There are rumours that at the crossover some 210s had teardrops or some 225 had square mirrors but that's the rule generally. Also the 210s had black "R" badges whereas 225s had red ones. Inside the 225 has a chunkier steering wheel with a red "race style" band at the top. I'm sure there are other more subtle differences but you'll find plenty of threads on here about this. It's been done to death. Earlier cars had tape players, then they had CD changers and then the very last cars out of the factory had CD players and a Tracker fitted. (like mine). Also the colours changed too. Red changed from Flash Red to Emocion red I think and later on silver was introduced and then Platinum, originally as a limited edition and then virtually all the run out cars were Platinum.
The Recaros were an option on all LCRs. Satnav was also an option and much rarer. Apart from that the specs you'll find should all be pretty much the same.
I hope this helps. Good luck in your search, you've come to the right place to start looking. You might even find one on here in the classifieds.
Right, now everyone else can add the bits I missed........