Depends on what your goals are for the truck. Interesting swap. I'm largely ignorant of what the power limits are on the autos; most people swap to manual transmission. I haven't ever heard of anyone extolling the virtues of the Nissan auto transmissions in S-chassis cars. I know they're heavy AF compared to the manual counterparts and for the S-chassis cars at least, kind of kill the spirit of driving a sports car IMHO. I know the manual couldn't hack it on my KA-T build and I ended up swapping to a Z32 manual transmission around 400whp/wtq FWIW.
You're in luck. This site hosts the factory service manuals for most nissans. I'd download anything from 1991-1994 for the 240sx and it'll have the pinouts and routing for the harnesses and an AT chapter to cover the slush box. Beyond that, I'm, not a ton of help on that transmission. Hopefully someone more experienced will chime in.
As far as question 2 goes, yes, there is a SUB harness for all of those accessories. You can get one from wiring specialties or make one of your own, it's not hugely complex.
Unfortunately theirs is for the manual transmission. You could modify it or try to locate one for an auto trans maybe from a junk yard? didn't really find much in a cursory check on ebay.