Custom build questions

electric, water and dump, all go on drivers side
IF you stick them some place else, you will have trouble in campgrounds
especially those with specific arranged parking

the fixed mounted frame propane is usually on that side also

portable bottles can go where ever you want, batteries, generator same thing, any place , either side

Generally all utilities are on the driver's side. The NEC basically requires that the electrical inlet be on the left side, towards the back, although it does allow a little leniency for exceptional cases.

The tanks themselves can be anywhere convenient so long as the fill and drain fittings are in an appropriate location. Generally it's preferable to have them somewhat centered so that the weight is more or less equally distributed to both wheels when they're full.

mine are all on the drivers side, most dump stations are set up that way too.
you might want to go to an RV dealership and check out all the units to help answer your questions post some pictures when you start the build