For a stock block 2jz-gte with 900whp, I'd start with a 71mm+ modern turbo. Your peak power will probably happen closer to 7k rpm give or take, but ultimately this will keep your peak TQ down, and keep the stock rods happy. Afterwards, I would be looking into a pair of matching camshafts to the turbine you plan to run, and an intake manifold to free up the restrictions at that HP, and to have a nice powerband to match.
Personally, I like a Intake manifold that has been modified with a larger plenum, such as Titan/SP/PHR/RSP, ect, because it frees up some top end, but helps retain some bottom end TQ by keeping the factory long length lower runners. However if you like all that top-end, plan to run 12 injectors down the road, or having an option to run a big TB without adapters, or simply the looks of a short-runner FFIM, then there are fantastic options such as CPC/Hypertune/Greddy/Veilside(Unicorn), ect.
For electronics, it's a little early to say because of the MKV being a modern car, with modern BMW electronics, I wouldn't be surprised to expect some challenges from swapping an older motor into a newer car and keeping all the body electronics happy, if one were trying to build a street car. For instance, I'd probably start looking into a modern EMS that can run a PWM controlled high pressure Direct injected fuel pump, and DBW because the MKV is DBW from the factory, so you'd probably want to run a DBW throttle body, unless you wouldn't care to hack into the car to run a cable setup, which wouldn't really make sense, given the advantages of a properly setup DBW.
A couple of modern EMS that I can think of on top of my head would be AEM Infinity/Pro-EFI/Motec, ect, but it's also really important to factor in the availability of tuners that supports that EMS, otherwise it'll be an expensive paperweight.