What is your whp goal not bhp goal again?
If you just want 550whp aka 640 bhp, assuming a 16% drivetrain loss, high quality upgraded twins and charge pipe meth and 93 will get you there.
You could make 550whp single turbo only but you would not like the lag and would be using a larger turbo then you need. Small powerband + too much lag.
I would also ask where your whp goal comes from. Power to weight to your cossie etc. An n54 can make 550 bhp on stock twins, granted they may not like it
Making a new IC and charge pipe sounds like a PITA when off the shelf huge ICs which fit fine are available see the bms/vrsf 7.5 race stepped IC. Huge heat sink. It will cost likely more time & money to make the type of system you are talking about with zero performance gains vs. What is available on the market today.
The road to 550bhp or 550whp is well known and I would say decently documented but we are all here to help share our knowledge. For the power it sounds you want to make my vote is stick with twins, stay the fuck away from mmp, vtt, frankenturbo, daw, or other China cast turbos. Unless you get them balanced state side and possibly upgraded(internals/wastegate etc.)...which removes the values of cheap twins given the insane install cost. Even if you do turbo replacements yourself you have a down car while waiting on an rebuilt turbo when the cheap twin goes bad or more than likely have to buy a new turbo as most companies aftermarket twin turbo warranties are questionable. Some china cast last 3k some 20k. There is a whole facebook group devoted to cheap china twins and how to make them reliable/where to get rebuilt/where to get balanced in the States.
All that said...twins are inherently 2x as unreliable, if not more, than a single. But for your relatively modest hp goals tier 1 high quality twins should do the job: RB or Pure are the only proven good solutions imo.
Also, please visit the octagon to see reviews of various turbos and the members who may or may not support them

the discussions can get heated which is why they end up there.