If you are doing all this building a 2 wheeled trailer it's really more cost effective to buy a good used one strip it down and add to the existing frame as you see fit for your needs.
I bought a new Schwinn Mark II for around $140 remove the cover and use the frame as is.
I have one for the grand kids and have put 160 lbs. in it and rode great.
You don't need to worry about all the stuff like hubs, wheels hitch as it's done already for you, you have a base to work with at much less than it would cost to build one.

You have already bought $32+ worth of stuff you could have made if you are really building the trailer?