My neighbor has the sky lights that based on tubes from the ceiling to the roof. I'm amazed at the amount of light they conduct. You should consider putting your lighting high, about 9 feet, and on the walls rather than the ceiling. You'll be glad you did.

Why can't you back in? That will put your RV electric on the same wall as the sub panel. The good thing with driving in is that you don't get exhaust in the garage. Is the door going to face the road?

Put in a dump connection, if you are allowed to do so. A work sink is a nice option.

Are you putting in a roll-up door or standard garage door. The standard door comes in insulated form. And yes, they have automatic openers for standard doors of the size.

If you go for windows, consider placing them a bit high to deter bad guys.

Make it wide enough so mine will fit too ;-)