I will probably go with all the fresh, gray, and black water tanks if I decide on having a bathroom in the bus (which I will most likely do). However for the Races they really don't care what kind of rig you have as long as your not dumping waste on the ground and its not a safety hazard
. But seeing how this will also double for occasional camping I would rather have the tanks then not have them.
As far a priority goes the tanks and bathroom are not at the top of the list because there are restrooms available at the races. The bus will probably be an on going project that depends on available funds at the time. (I'm a Photographer and student that's getting married in May and will be a step-dad to a seven year old, that all equals out to .....BROKE.)
At the top of the list is to first get a bus
. then replace the floor, build bunks and sitting area. once those are in then at least it would be ready to go to the races with the bare minimum if needed. The rest would be built as time and money permits. Come on lucky lotto!!!