1) Applications aren't open yet. At least not for air force. Should be any time now.
2) You need a nomination for each academy that you are applying to. Whether or not your congressman/senator will nominate you to more than one academy, is totally up to them. Some will, some won't. A representative and senator is ONLY ALLOWED to nominate 10 people for each of the academies. If they have a lot of applicants, they may only nominate you to one, so they can nominate another person to a different academy. NO ONE HERE KNOWS THE ANSWER TO YOUR QUESTION. That is totally up to your representative or senator. You can ask their staff. Or look on their website. They can answer your question.
3) FYI: The coast guard doesn't require nominations. They choose all appointees based on their applications and the coast guard's requirements. All other academies require nominations.
4) No, they don't frown on you applying to other academies. And most representative/senators want you to apply to as many as possible. (Again, they can only nominate 10 people per academy. If you put more than one academy down, you have a better chance of getting a nomination. But you better want to attend that academy if you receive an appointment. If not; don't apply).
5) The only advantage to applying earlier than other people, meaning in the July time frame instead of Oct-Jan when most other do it; is if you happen to be the individual that has an application that walks on water. You're a 4.0gpa (Or on the edge); kicked butt in the SAT/ACT; nailed the CFA to the cross; have absolutely no medical or physical issues "At all"; are ranked in the top 1,2,3 of your class; basically, the type of applicant who is going to be accepted to just about any college you apply to. If you're this type of applicant, then applying early can be very beneficial. It opens the door to you for a Letter of Assurance. "Military version of Early Acceptance". Basically, they guarantee you an appointment. You still have to receive the congressman or senator's nomination. (That's federal law). But as long as you have the nomination, and pass the physical, you're guarantee the appointment.
DISCLAIMER: Even if you're the very first person in the country to complete their application, that doesn't guarantee you a Letter of Assurance. Just that it opens the door for one. The earlier you've completed your application, the better chance you have for an LOA. Mind you, only about 10% of all appointees receive an LOA. It's just the academy's way of trying to get you to commit and not apply to other colleges. It's rare, and you have to be one of the best of the best of the best.
Hope this answered most of your questions.