Welcome to the group
I am an Amerigo
wanna-be as well and have been looking for a decent 16' for some time without success. I saw one in TN advertised for a while but that was a bit to far to travel.
About your questions: That part is a tensioning bracket for the spring bar on a weight
distributing hitch. There should be one on each side, but not to worry, it is a part of the hitch, not the trailer itself. Due to it's fairly light weight
a WD hitch usually isn't needed on the Amerigo
I don't know what you want in a floorplan, but rest assured that almost nothing is available. Let us know what you want to do and you will get a lot of help.
I have a sales brochure for te 16'er and that's about it.