# 1, I would do myself for three reasons. First, no one will clean it up as well as you will, since you will be living in it! Second, it's a great way to learn your way around your coach, familiarize yourself with all areas, and find things that need fixing/adjusting. Third, you will save a TON of money doing it yourself.
# 6, Inverter switches will only work if you have the battery bank (size or number of batteries) to support your power draw, AND your batteries are good. You need to do some research on what you intend to power, and what your battery bank will supply, or what additional space is available for more batteries.
Size of Battery Bank is a personal decision, and will be driven by how you use your coach. Ie; if you boondock a lot, you can probably justify the $$ to put in and maintain a larger battery bank. If you travel from hook-up to hook-up, it's probably not necessary.
Good luck in your journey!