Most of your questions have been answered already. I run 31" tires right now.
Lifts available: Old Man Emu (Firmer than stock; ~1.75" lift), Iron Man (Stock type ride; ~1.5" lift), AC Springs (Very firm ride; 2" lift). Krypton Subframe drop. Can use stock springs for stock ride, or combo with lift springs.
Aftermarket support? Limited, but the community is very supportive of homemade modifications and ideas.
The R50 as a whole? Nissan built these things pretty tough. 33 spline from transfer case all the way to rear tires, front hubs are 28 spline. Still very tough. 3.3L engine is tough and takes a beating. 3.5L is just as tough but has much more power.
There is a lot more, just check out the threads and stickies.