Hi Elspeth, it's always nice to have another Texan join our ranks. Welcome to the Skoolie madness
i'm going to take the chance that no moisture will get onto my bus floor and am going with a wood pergo laminate t&g flooring. As far as tile flooring goes I read somewhere that they make a flexible grout these days that might work well to help alleviate any cracking.
Like Tango mentioned plumbing is fairly straight forward but electrical can be quite complicated and if done incorrectly it can be deadly. I have a build on this page called "Southern Comfort". Feel free to following along for ideas and tips/tricks on how to make our Skoolies livable.