You'll hate it I believe, it's not fast at any means, or even fun to drive.
My e36 325is got 27-29mpg constantly around town and avg'd 32 mpg on my trip to bimmerfest last year. I would say e30's are much more forgiving, you can push border a lot, where as with e36's they can easily be pushed too far and cause you oversteer like a mother bitch.
Oh and you're not gonna get a 4 door e36 down to 2800 and drive it comfortably. Correction the motor does not sit further back, it actually sits farther forward, which brings the transmission forward, it's just not as long. If it was actually pushed back like the six cylinders are the car would handle so much better IMO.