i can't answer all of your questions, but i'll do my best.
1. I have no idea
2. i bottom mounted mine on a 3/4" wood panel, the long shafts seem to be the right lenght this way, but make the throw way too long for my taste. i'd recommend routing out some of the wood and using the regular shafts...or the long shafts with a restrictor maybe
3. yes, the u360 does support shifted commands
4. i have no idea
5. i can't compare it to the p360, but i can say that my wife abuses my u360s when she plays pacman and they have held up pretty well. i have had no problems with mine at all. i also caught my 2 year old hanging by them. (one hand on each joystick, just hanging there...i was not happy, but they are working just fine)
...u360s rock..