Your direct questions - boost will vary on your build / injectors / other factors and will be decided on a dyno tune. You can run 3sgte or 3sge or aftermarket camshafts, this will vary where and how much hp you make.
Speak with wtf auto as to local advice/specialist.
Depends on your driving / performance requirements. Mr2 is a personal choice. Options options
3sgte build. Requires so many components and costs not listed, clutch, dyno time - too many to list before even the nice to have like e153 gearbox etc. I have reservations at your cost vs outcome. You would be best finding a smashed mr2 turbo to put everything across, or caldina (gen4 swap, injectors, ecu, plug and play almost).
Realistically if you want 3sgte sell your mr2 and buy a turbo car for your turbo fun, there are many differences in brake components, options. Turbo cars are for sale, freight to wa from east coast around $1500.
2gr - 2grfe - $12-$15k for amazing drivability and low rpm power (will out perform 3s build spec). Use your car for the transplant. If you destroy the engine they are cheap off the shelf.
K20 swap. K20a engine / donour car with ecu etc, conversion kit from Hux Racing. Little more voodoo to K20a swap. If you destroy the engine they are cheap off the shelf.
5sgte. 5sfe block, 3s head. Stroker pistons, head gasket, aftermarket ecu etc is similar costs to your proposed 3sgte build path / costs. 5s blocks can be found for a couple hundred and is about the only additional to your 3s build path. More drivability, more potential. This will likely be more expensive than options above, depending on build spec, however potential depending on turbo selection.