Looks like some good work so far, you're pretty brave to take on a job like this! Props for including the full parts list and extra photos as well.
And I decided to answer two of your three questions :)
2: A friend of mine swapped the auto box from his Nissan S15 to a 5 speed manual. Preferred the feeling of driving stick / ability to stay in the rev range longer etc. Also, useful for doing donuts :P
3: My cousin had a Ducati Monster. All I know is that it scared the hell out of him. He sold it after a short while and got a 66 Mustang coupe instead as his "weekend toy".
A manual can make almost any car fun, at the expense of the clutch that is. You're friend is nuts for doing the swap. Only a maniac who really enjoyed his car (or was broke and had a lot of time) would do a swap like that!
You know, when I read " he sold it" i just shook my head, but replaced with a 66 Mustang! I remember there being a 66 1/2 mustang too. Not sure what the deal is, but if I could afford it, I would daily drive a classic mustang.
Haha, he was a professional drifter in our country, and had a lot of free time, so it's what made him happy I guess :) He did the swap in his garage, and it actually seemed pretty easy. Only downside is the dash still had the PRND markings.
I did a full photoshoot on it a while ago (pre-gearbox swap), you can check it out here if you fancy: https://steemit.com/photography/@garethb/searching-for-silvia-shooting-the-nissan-s15-original-work