1.If ur running a big laggy turbo w/ a fully built motor, then yes, nitrous would help against it and be nice to have, plenty of drag cars use it for just that, as the nitrous goes off ur hitting full boost.

2.From what ive heard, i think b&m makes really good short shifters

3.If your looking to make over 280-300 hp, then yes, i think you do need it because ur stock one doesnt flow enough or something like that.