Welcome,Good looking bus,
Am I suppose to split up the shower and toilet
It's your skoolie, you can do what ever you want. There are a lot of
pictures on this site about how people have done theirs. Personally my bathroom and shower is a full width room that you have to pass
through to get to the bedroom. There's just two of us, and we've been sharing a bathroom for a looooong time. If there are rugrats involved
you may want to split things up.
As has been said, it's best to have the toilet directly above the black tank, and have the waste dump on the left side. Only because that's how
most dump stations are set up. The rest of the stuff depends on your plumbing skills.