Lou, I am impressed. Sounds like you have everything covered. I can't find anything wrong with your plan. The only thing is the bond wire does not have to be 18" deep in a trench. It literally can be on the ground. I usually try and get it a few inches under the surface since typically it is well away from any traffic areas. If it is in a traffic area then several inches down would be a good idea.

keep in mind that you can't share a bathroom ckt. with another room. It MUST be dedicated to the bathroom only. It can be used for power, lighting, a fan, a vent and/or whatever within the bathroom. As long as the ckt supplies devises located in the bathroom only.

I was told Number 8 wire was only sold in Romax form in the 8/3 with ground, so now I have a black, a red, and a white wire, plus a ground wire that is a little skinnier. Do I just ignore the ground wire and use the white wire as the ground? When using 240v, do you ever need a neutral?

Electrically, and assuming everything in the system is switched together (i.e. no unswitched loads), your hots (black) will all be joined. Your neutrals (white) will all be joined, and your grounds will all be connected to each other and any boxes in the system that are metal. Assuming you want it to meet code, you cannot have junction boxes that are inaccessible (i.e beneath an attic floor or buried in insulation). Dan