In a nutshell. Since you are in the US you are lucky. As these parts can be sourced locally and pretty cheap. Buy a local T series rear end out of a TE27 as it is the correct width and is already leaf spring. TA22 is wider and coil sprung (unless very early. An early (Zenki) LSD centre will bolt in possibly needing to shave the axles. If you want to convert to disc brakes that's up to you and you can research what fits. You may want to pay someone to design a fancy axle location setup if you are really going to have that much power. There is no such thing as rear struts in this shell.
Buy a TE27 pedal box so you have hydraulic clutch to suit the later T50 gearbox. You can put AE86 derived coilovers in but will need TE27 steering arms to bolt them in. It will affect your front geometry as the stub axle inclination is different so you need adjustable camber tops to pull the struts in. Can only do that if you have coilovers as standard springs will hit the strut tower.
Front crossmember will need to be modified whatever it comes out of. A 4A engined donor crossmember will be too wide. Have a look at local Starlets, some of which I think already have rack and pinion, and are narrow, but you will still need to do some fabrication there including modifying the engine mounts to 4A and connecting to your steering column. It all impacts steering geometry and is more complicated than it might seem.
A tail shaft will need to be custom made as anyhing factory fitment will be too long.
I disagree with KE70Dave about the wiring to the ECU. To get it all running properly is complicated and will directly impact the driveability and practicality of the car. If going any bigger than 270 duration cams, or fitting ITB's as you say, will require an aftermarket ECU. Not sure what smog rules are in California now but you may want to look at that first. A lot of people build cars to 95% completion, then sell them because they can't sort out the engine management properly. In a standard AE86, there are three seperate looms, engine, dash and body. If they are incomplete or not talking to each other, the car turns into a pig.
Any fuel setup is going to be fully custom with the items you mentioned. The fabricator can work that out.
It's going to cost you a LOT of money if someone else is doing it.