Well, to be honest, NA supra > NA skyline, T supra > GTST skyline. Although they are heavier, they can seem to beat a skyline in a straight line, but I'm pretty sure skylines are more fun around corners. I like my R34 coz of the looks, that's why I chose it, with the money I had, I coulda bought a TT supra or R33 GTR. Just depends on what you want, looks, handling, power, budget.
Yes, I'd advice you to look into R33's, over R32's. Because of age, tear and wear. When I say R33, I kinda don't mean series 1. It's hard to find NA R32/R33 s1 in really good nick. Have a look around for series 2 R33's or even R34's. The price different between the 33 and 34 is maybe a couple of thousand, but if you have enough, then R34 would be worth it.
But I wouldn't suggest you to buy an NA now and do an engine conversion later, because it's not worth it. Better off selling the NA and buy a turbo. Unless you seriously can't live without your car lol.
R32,33,34 GTS25 / GT25 = RWD
R32 GTS-4 = AWD turbo
R33,34 GTS4 / GT4 = AWD NA
R32,33,34 GTST / GTT = RWD turbo
R32,33,34 GTR = AWD twin turbo
You pretty much got it right, but just remember that a R32 GTS4 has a turbo in them. Apparently, there are some R33 GTS4 turbos, but it's really rare. Someone on this forum has one.