X5 N55 PWG Big Turbo Tuning Options

[LSE31]

Hi all, toying with the idea of tossing a GTX3582 on my 2012 X5 N55/8HP combo. Goal is 500whp. A couple of questions:

1. On PWG cars, what is the stock wastegate open pressure NOT accounting for the electronic controller? Raw opening pressure
2. On the topic of wastegates, is it possible to run an external gate off of the factory ECU without warning lights? GTX3582 and other turbos I'm looking at are all external gate only.
3. How do the various piggyback systems stack up as far as tuning for a bigger turbo? From what I've seen of the interfaces on a couple of them, they seem to be limited to peak boost and WOT fueling settings, which seems severely limited.
4. From what I've read, a completely stock N55 should handle 500+ just fine (barring supporting mods, obviously), as should a stock 8HP, but all the information I'm finding is from RWD coup/sedan applications, anything in particular to be worried about on an AWD E70 X5? I know the transfer cases in the previous generation were a big weak point, unsure if they addressed that on the E70.
5. High pressure fuel system; what are the options for pushing it to 500whp? Most of what I've seen is people recommending just converting to a standard port injection system, but I'm very unclear on this.

Not interested in hearing "Just get a FT/Pure" unless you want to buy it for me. I can buy a GTX clone for $250 and attach it to the engine with a bit of scrap pipe and an afternoon of work.

Thanks!