1. There is nothing wrong with 6 volt if you have heavy cables and keep the connections maintained.
2. 16" 8 hole trailer wheels will fit it. Newer 8 hole have a different bolt circle.
3. I don't care for automatics so someone else can answer your question better than I can.
4. These guys make reproduction beds and do a good job of it.
http://www.mar-k.com/ I would suppose they sell just the pieces you need.
