Supra newbie questions.

[supra90turbo]

Well, GE pistons are like 9:1 comp IIRC. Not that high. You can NA-T the thing for cheap using all turbo components. Intake manifold, exhaust manifold, turbo, downpipe, intake, afm, wire harness. It'll plug right in provided that you get the same year harness. If it's an auto, then I'd upgrade that to an R154 out of any MK3 Turbo of any year.
While you can use the W58 5spd that is from the NA supra's, it's not recommended if you plan on making more than 350whp. It's weak to say the least, it'll handle power if you treat it like a DSM trans though.

If your GE is in good health, I wouldn't hesitate to turbo it.
The only thing different between the GE and the GTE block is that the GTE has oil squirters, yours doesn't. Not a huge deal as the GrpA engine's didn't have them either, and they saw relentless abuse.

It'll last a long time if you monitor your vitals. Some water injection wouldn't hurt either