The collective noun for cadets is a corp of cadets.

No, Air Cadets do everything the army cadets do, (Shooting, Drill, Camps, etc.) and more, The Air Cadets do all of those things as well as flying.

Girl Scouts in the US in grades 6 to 8 are called Girl Scout Cadettes.

There are other types of Cadets, such as an Air Force Academy Cadet, and yes, girls may be that kind of cadet also.

Yes, Girls can be in cadets, for instance: Air Cadets, Army Cadets, Marine Cadets, Sea/Navy Cadets or cadets which are non-military such as Girl Scouts etc.

Same thing - cadets.

This would depend on what you think, this is a personal opinion question. however people like The Prince of Wales, Prince Charles did say "Air Cadets is the Biggest and best Organisation out of all the cadets" But yet again it's opinion

Well being a corporal in army cadets but my opinion would be to pick army cadets but air cadets are just as good as army cadets with the bonus that air cadets get the chance to fly helicopters!