1. The best person is Wags, by PM
2. He will go through these with you depending on your proposal
3. Again Wags will clarify depending on your proposal
4. Simple mod won't get you access to any technical help apart from on pubic forums. And you can't sell it.
5. Yes, and that depends on what you can show to ED/TFC as part of your proposal
6. As Wags has said, there is nothing stopping one developer producing the same plane as another.
Basically, you need to prove to ED that you have something to offer. Just PM'ing Wags saying, hey Matt, I have a great idea for a add-on but have no idea how to do it, or don't have a team to do it etc is likely to get a polite refusal.
To give you a simplistic idea of what you need to develop a 3rd Party Add-on:
3d modeler
LUA coder(s)
Skinning artist
Manual writer
Someone who understands schematics of fule, electrical and hydraulic systems and then be able to code that.
Hope that helps.