This is another one of your questions that depends on the aircraft/payload/airport........
1: Yes its done, although some aircraft have automated systems whereas if an engine fails the pack on the other engine/s will automatically shut off.
2: I've seen around 150 kgs on our small jets up to 6,000 KGS on a 772. (Many years ago, APU takeoffs weren't permitted in the 772 so it was PACKS ON or nothing, but that has since changed)
3: No idea.
4: Yes and if the takeoff was on a contaminated runway, you might find that the stopping distance is based on them using that other thrust reverser/s.
Mutt