Check out https://cagekits.org/product/a90-supra-roll-cage-kit/
That is the only cage kit I have seen for the supra besides bolt ins. I also believe P2uned is selling some type of weld in cage but I think its more drag race based.
Go with Pure. I believe even Titan has switched over and last I heard they were trying to keep some in stock. I would say go stage 1 and skip the 0 but that's just my opinion.
I used my stock driveshaft down into the 1.3 60 fts at the track with no issues. I done the DSS Carbon shaft and I haven't noticed any noises or vibrations. However I will tell you its not just bolt on. You have to change the rear pinion flange which will require a pinion flange service kit...
Unless you are really planning to push the car, the 2 port head will be fine. There are stock,(completely untouched) 2 port motors in the 8s. However they wont live there regularly they can achieve it. I believe the 6 port head will help with cylinder pressure issues in the long run but once...