If the motor is running, and everything is working properly, the bus doesn't have to move for the alternator to charge the batteries unless you have an alternator that is hooked to the axles.
For my bus, I plan on having a separate battery bank, because if the lights, computer, tv, etc. drain them down, at least the bus will still start.
Go read A LOT about RV solar power systems, connections and design. You will fry your panels, alternator, batteries and so on if you are just going to connect wires and go.
Unless you have the equipment and experience, I really don't think splicing battery cables is such a great idea, considering how much power they handle. I have no idea what your budget is, but it would be better to go buy premade cables for chaining batteries together than just twisting 0 gauge together with some electrical tape. You can buy battery cables and connectors at any auto parts store, most hardware stores, Wal-Mart, K-mart, Target, Lowe's, Home Depot, Menards, Runnings, any trucking supply store, 4x4 store, or a ton of places on line.
Are you going to run the batteries in series or parallel? How are you going to isolate the panels from the alternator? Are you going to match the amp-hour rating on the batteries?
For your extra question, since I don't know what you do and don't know about your dash, I have no idea how to advise other than disconnect the batteries first.