What I should know before buying an E30

Hey there. So I'm 18 years old. I'm mechanically inclined as in i know how to take something apart and put it back together again, but I do not have an automotive technology education. I'm actually working towards that in January.

I have did all sorts of reading and watching and learning about the E30 car. It seems to me what I would want is a 91 325i swapped with an M50 from an E28. Please do correct me if I'm wrong

I want something quick and reliable, but not too hard to work on. I've read some of the DIY walkthroughs and I feel like I could do it, but I want to hear from the community.
I've got about $4000 to spend,but I would have to sell my current car to get $3000 of that $4000 (I drive an 85 corolla with 91k original miles).

Should I go after an E30 now? Or wait until I'm past the motor and Manuel/auto classes which I don't be through until the end of 2016?

I wish to hear all of the wisdom from the community.

I'm located in Louisville Kentucky and I do a lot of highway driving so I do know for a fact I want a Manuel tranny.

Please help me out as much as you can!

(BTW I'm looking to make an E30 my DD and also a life long car, its my dream car.)

What I should know before buying an E30