Help I'm confused!

Ang daming models ng BMW! e36, e46, etc. etc.

316i? 318i? what are the differences?

what's m-sport? how do you differentiate an m-sport look with the real thing?

I'm looking to buy a late 90's or early 2000+ model. i'm confused about the models.

which one is the better buy? i know practicality is out the door since maintaining will be quite costly, but which one is bang for the buck? 500k-600k budget.

which one is more fuel efficient? does one specific model have a recurring problem? matibay ba 'yung mga late 90's early 2000s?