Trailer wall construction

[K100E]

After 3 years I finally was able to pick up a very clean 98 Kentucky 52X102 that I plan to use to haul my sled truck around in. I want to build living quarters up front with a shower, toilet, sink and bed(queen size if i can). My question is the walls have E-track over them and knowing past history from my father they can support the weight of a small car seeing as hes done it before. What thickness of what material should I use around the area? 1x2, 2x2 or 2x4 pine wood and cover with what?? Was wanting a wood wall finish, anything but white that makes me feel like i'm in a nursing home. On the upper deck area(5th wheel plate area) i wanted to put the bathroom to over hang off the deck to allow a strait drop to the black tank mounted in the belly box, on top of the bathroom area i wanted to build a small loft to hold the bed overhanging the rest of the trailer(rear to the entry wall) should I frame it out of metal tubing and attach it to the trailer? or for weight saving just frame what i need out of metal which would be the bed area and use wood to cover the rest? Would it be better to move the bathroom to the front of the trailer and raise the floor? Any help would be great. I've spent 3 hours on the internet only to find people converting trucks, box vans, or cargo 1/2 ton vans but no one who has detailed pictures of a semi trailer thanks in advance!