I honestly haven't gone down the RB worm hole. another hurdle you may face is the cost of abused old transmissions. w58's from 2nd gen supra's are what r154's use to go for a few years back which is utter silly tbh.
a straight forward route would be cd009, stock vq35 from 2nd gen g35's for better head flow, variable timing cam lock delete, turbo, aftermarket ecu, and let er rip. forget affordable 2jz and even with solstice trans now. solstice trans were 800-900 as of last week and then add in the cost of bellhousing, flywheel, etc.
did a quick search and the z31 suspension can use s13/maybe 14 suspension bits with random parts from other nissan models here and there. another research route can look into the infiniti m30/j30 suspension swap parts list. pretty much just searched z31 suspension swap. there also maybe some more options with z32 suspension bits.
the nissan, toyota, mazda suspension swap parts have a alot of options. also i think the z31 can use the j30 rear diff which is considered the big dog for rwd bolt in irs parts for nissans and front sub frame swaps to get several japanese engine options. just depends on how much you want to tear into the car honestly.
many of the 2nd gen supra folks i talk to here and there always say to spend money upfront for a car in better condition upfront and worry about the rest later.