Ok, well before you go upgrading the turbo, get some type of EMS. Since you are looking at big numbers, you may want to get something with some type of timing control. If not, at least get an SS AFC v2, so you can get a decent fuel map and have the ability to data log. With that being said, your gonna need a Wideband of some type. I have an AEM which works fine but I hear that there are better ones out there for a good price. You may want to look into a clutch and flywheel combo since you should weld your lsd. Exedy stage 1 is a great stock replacement but only rated for 320 ftq. You may want to look into spec for a higher rated clutch that is still a full disk.
With all that being said, good luck with your build I really hope it works out for you. Its always better to do it right the first time and get it over with vice taking short cuts and costing big money in the future.