All the questions you asked are answered in great detail in other forum post. Use the Search function and read, read, read. You are just asking us to repeat what has already been asked, but without any details on what you plan, or if you even know what you want. You are just getting tid bits of info on this string...
Is your "tongue" battery the big one, or are you talking about a small hold-in-your-hand battery which would be specifically only for the trailer brakes? You can get a ticket for not having 12 volts at the emergency break-away device for the brakes.
After you read a few post on solar set-ups you can ask better questions if you still have any... There is everything you need to know on this forum