I'm not the lift specialist by any means on this forum, but 4" is a pretty substantial lift. I am pretty sure that you will need a slip yoke eliminator to reduce driveline vibes amond other things, but maybe not. Hunter?
Also, once you get a lift that high, new (very big) tires are inevitable if you do not want to look extremely awkward. The mods will never stop, and it can reallyyy hurt the budget. More power to ya though!
As for the 90mph, with my stock height 30x9.5" ZJ, 90mph seems a little shaky..I couldn't imagine it with 33's or 4.5" of bump.