I did my electrical outlets the "old work" way and cutout the box holes after the boards were back up. I did have the wires in the walls ready and in place to pull into the box, so is was just the box. The box flanges attach right to the plywood easily (at least in my case it was). I only had 5 110VAC outlets in any case.. so not a lot of effort. 2 of the outlets are in the appliance stack-up cabinet where the AC and Fridge plug in, so I mounted the boxes on the walls instead of flush. Just the kitchen and bathroom were flush to the walls.
I'd be careful with the laminate floors for the reasons you mentioned. I was going to do something similar, but screwing the walls down over the top of them doesn't allow them to float and they may buckle. If you want to use laminate, I'd build the walls and then put the laminate down as you would in a house with existing walls so it floats. More work for sure... but I'd be worried about the buckling otherwise.
I did not end up installing floor planks. I went with the tread plate textured rubber floor. I am really liking it. Easy to clean... no worries about water or buckling. I think it looks nice and fits the style of the toy hauler. I do have a couple throw carpet mats I use in the bathroom and kitchen area... they are easily cleaned and look nice. I put the rubber floor down before I built the walls... easy install (as I remember... except for the glue fumes).
I installed it on the ramp as well which is my back wall.

