Great write up about your journey and the bike. Keep it up.
For your shifting problem my advice from personal experience is you should not be perfectionistic about getting this bike to shift to all gears. Lower end bikes with a triple often are hard to get working just right through all the gears. Sometimes I think Gripshifters make it even more difficult. The worst case scenario is get an old set of friction stem shifters and you can do whatever you want with the bars as well. Just keep getting get out and ride and don't let some of the issues get in the way of your fun. Your LBS should have all the tools you need for replacing bears on your botton bracket. You might want to try taking it apart nd greasing it up and see if that takes care of the problem you mentioned.