Lots of people have successfully built a TD trailer with no previous experience. (It helps if you have a friend or relative with tools and some wood working experience.) If you screw up, remember it's often easier to make a new part than trying to make the bad one work.
Do at least some planning for your interior cabinetry so you'll have something solid to attach it to on your skeletonized walls.
Surface mount electrical wiring conduit can be used for electrical. Not too expensive, not bad looking, you don't have to have everything worked out before you start and you can add to it later.