Couple others answered the question better than I could. All my experience in building a car is from the Mk3, same concepts, often different vendors and brands though.what bushings would need replacement in a mark iv.. also where to get them from? what brands make them? thats something i will need to do..
For reference, if it's made of rubber, it was replaced on my car. Everything on mine is urethane, with the exception of one particular bearing in the rear suspension that I believe is a Toyota replacement. Not sure if the Mk4 has that same issue, I know the suspensions are similar, but unique enough that I'm not well enough informed to give solid advice, sorry.
Either way, end result? I autocross my Supra, and it's a hoot. Between all the suspension work (really nothing exotic or anything, just poly bushings everywhere and tubular control arms where available), and the OS Giken diff, the car is VERY easy to control, and once it's dialed in, there really aren't any bad behaviors. I've only spun the car maybe three times in... hundreds of runs?
All that said, my wife's Mk4 still handles SO nice, despite being largely stock. I can imagine if I do the same mods to her car (if she decides to go that route someday) that I did to mine in the handling department, her car will be an absolute sweet heart to drive.