im trying to steer you off the diy route, been there done that and all, if your getting one built go with what works.
trouble is specs are hard to find as they dont want you stealing there development work, understandable.
from what i remember the autolusso hybrid and jsjtd may be the same one from same company ? like i said fitted and mapped not a bad price, you build something else and the mapping will most likely be a long affair to get perfect if ever.
if you do want to diy id say at least a 52mm compressor wheel, extended tip could get larger 54mm maybe if not looking for high rev high flow go for a smaller trim ie inducer , surge less low revs. or go far a small trim 56mm compressor.
the machining is doable for you , as it was for me , i measured and made my own tools and got a local machinist to do the bores as a large lathe is required , no hobby stuff.
the build and balancing is the important bit and as stated the warranty is what your buying.
make sure its large pad thrust bearing, advise its staggered gap turbine seal if optional, buying parts and wheels could be a minefield , again you build it and wheel blows 1000 miles in come back i dont think so.
contact jsjtd on here he will steer you better than i could.
ps are you mrgreg on fiat forum message today?