A lot depends on what you need for a trailer. If you need a summer camper, and have a good way of keeping it safe and dry in the winter, a light weight is OK, but if you want to travel all seasons where it's not -20 and you like to bounce it about and nothing happens to the insides, then a heavier weight and tougher trailer will be needed.
Many of your questions can be answered by just looking at the underneath of your intended rig. If you see a unit that just has panels underneath, and you are not looking at tanks and drain pipes visible, that is a tougher rig. If you look and see tanks, and flooring up to the height of your living area, well, you are looking at light.