To answer your first question, the 328 is not classified in IT. The E36 325 is classified.

As for 7-10K, the previous advice to buy is spot on. If you really want to build, pick something other than a BMW and pick something other than ITS. You will find tha a lot of stuff is just more expensive because it is BMW or ITS.

ITA is looking to be a good class. You should be able to find some good options there.