Turbo Banshees are a rare unicorn type breed. Finding one that runs consistently is even rarer. If you wanna know what it's gonna take, start looking at what the Snowmobile market is doing. Lots of success in that niche. There just isn't enough banshee specific builds out there running consistently well, and nobody is sharing the info for free.
First research the fueling needs of a two stroke. Then start reading everything on the Micro Squirt forums. Knowledge base is pure gold over there. I'd honestly try to get the EFI sorted out on a running motor before even boosting it. It'll be better to melt a NA motor then melt a motor and turbo as well. Maybe boost a stock cylinder set up first. Cheaper to practice on then a 521 mono jug set up. It's a rich man's game and even the best are melting parts.
Last, think very hard about how you intend to keep that boost in the cases. That's the part every one forgets. I've never turbocharged a banshee, but I've had my fair of turbo two stroke snowmobiles. The sled guys are ahead of the Atv crowd.