Different Output Voltages from Same Source?
Are there any gotchas to consider with this type of circuit, or is this the totally normal way of doing things (eg. like wiring a house out of a breaker box)?

That's a perfectly normal way of wiring it.

Is there a better way to do this?

No, it's how I'd do it.

This won't cause a short circuit, right?

Not intentionally, no. However it's always good to add a fuse or two to protect everything just in case anything untoward should happen. Especially where water is concerned.