wow....you have a lot of questions in there....
One thing that jumps out at me as requiring a response is your question about all the computers having the same IP address.
The way that works is you have your public IP address that belongs to your router, all the other computers on your network will have public IP's assigned to them (ie 10.10.0.0 or 192.168.20.10).
I don't have any experience with wireless networks, so I'll leave that portion of your post for somebody more knowledgable then myself to answer for you.