Hi,
The only one I can answer is the one about the mics.
Radio/ intercom systems are setup to accept either dynamic or electret. Dynamic won't work with an electret system and electret won't work with dynamic.
Unless you are flying old stuff the chances are you need electret.Even most old stuff has been upgraded to electret.
(electrets need the power).
Good luck with the rest of the questions.
How much are they in the states?
18