Unless you have fiberglass batt insulation in the walls, you can't run wiring in the wall. Best bet is to try and hide the romex cable inside the cabinets and protect with thin plywood or something for physical protection if needed. Upper cabinets typically have a hollow bottom in them that you can run wiring in. Cut a small access hole somewhere or remove a light (if you have one) and fish the wire through the existing hole. You can always pull out the microwave or even fridge to find a place to run wiring. Even under a bathtub or shower works. Once you start looking, there's lots of places to hide new wiring.
On switches, if you have batt insulation in the ceiling, you can run wiring around fairly easily. What you want to do is pull down any lights, AC unit bezel, skylight trim in bathroom, speakers, etc. in the vicinity of the switch you want to add and near the light you want to switch. You can use each access point you find to fish wire across. In our 1st TT, I was able to run wiring all over through the ceiling this way. The real trick is getting wiring down inside the wall. Once you find some access into the ceiling where you want it, if you can get a hand in there, feel around for a hole that might already be there through the top plate of the wall. I was able to find one. If you find one, you are way ahead of the game. If there is no hole you can use, you might be able to use what's called a "close quarters" drill and drill a hole into the top plate. Drill available at Harbor Freight. If you have a cabinet near where you want the switch, run the LV wire inside it.
You *could* use surface molding like Wiremold, but I'd try and make it invisible. You be surprised how easily it is to fish wiring around in a ceiling using even just the little holes behind the standard pancake lights.
I want to add a few switches in our new TT. If there's one thing I wish manufacturers would do, and they're all the same, is add wall switches for lights and fans throughout.