Hey mate,
pretty sure that r34 NA were never produced with leather interior, but you can pick up leather seat covers for about $500. There is a deal going on in the group buys I think.
When it comes to maintenance you will probaly spend more on a r32 simply because of the age of the vehicle. More prone to simple things breaking. You can pick up r34s that still feel like and drive like new.
beware however with buying NA Skyline, you may find it real hard to resell it, and the value of the car will drop so much quicker than their turbo'd brothers.....
good luck with your decision