It would probably behoove oneself to start off with as powerful a base engine as possible.
A 4A-GE 20V would make sense for the simple reason that it's a relatively easy swap into a 101, especially if you purchased a complete engine with the associated ECU, wiring, and gearbox included. CMIIW but swapping over just the head would lose you the stronger crankshaft and con-rods, higher comp pistons, and oil squirters among other things, although those would probably get shafted anyways eventually for custom parts in the quest for 350 to 400 horsepower.
A 3S-GE is possible (check out the TRD2000 for an OEM version, in a 101 chassis no less), and the 400cc extra displacement would make reaching 350-400 horsepower an "easier" prospect.
To get anything over 300 horsepower, regardless of base engine, would most probably require forced induction of some kind. Namely, nitrous, a supercharger, turbo, or combination. An N/A 2JZ, for example, makes "only" 225 or so horsepower in standard trim, and probably maxes out at something like 285 N/A unless you resort to wild cams, super-high compression, a displacement increase, a combination of all three, and/or magic of some kind (a phoenix feather wand might help here).
Just my two cents, shooting from the hip here brah. More experienced motorheads should probably chime in at this point...