Hey mate. ive got a R34 4-door. when i got it, it was tiptronic auto but i've converted it to manual and by far by anything the conversion went very smoothly alot of people cannot tell it was once an auto.
it is hard to find a manual GTT but there are still a few out there for sale its just a matter of finding the right one for you.
Space wise in the back is alright, not the best car for a family but its alot better than the coupe.