I had my trailer built by Hill Equipment in Marengo, Ohio.
1-419-253-2991, ask for Roy Hill. All they make is trailers. It will take about 4 weeks to build one once you are in the queue. They are open M-S, 830 to 5. They build trailers for many trailer dealers in Ohio, Michigan, Kentucky and Indiana.
I prefer surge brakes over electric brakes based on my experience with both. I service all my own equipment both sets of brakes require nearly the same effort to maintenance or repair. It always seemed like I worked on the electric brake trailers between 3 and 4 times more often than the juice brake trailers. Sure was always fiddling around with the controller too. The surge brakes always, always, always worked right, the electric brakes worked right, wrong or not at all. They always seemed to not work or work wrong when I was loaded and it was raining, snowing or dark.
A comment on load management, if your trailer and load raise the front of the tow vehicle alot plan on having a problem because you just moved most of your rigs steering and braking capacity off the front where it belongs. If your rig sways excessively going down the road the trailer may be butt heavy or the suspension in the tow unit is too light. The best way to fix this is to rearrange the load and check those rear springs on the tow unit. I absolutley agree that light braking will straigthen up your trailer if it's swaying, however this is a symptom of a bigger issue that can be addressed. What happens if a rookie is running your rig for you because you are too sick or sleepy to drive and it starts swaying and they don't know to brake or how to brake. My wife can drive my rig without any special instructions....
Construction note: BE SURE the tongue on your new tandem trailer comes all the way around and under the frame of the bed at least back as far as the front tire. A lot of trailer builders take short cuts here by only extending the tongue to the first cross brace for the bed. This will create a weak spot and flex point just under the place where the second heaviest part of your tractor is setting on the bed. This practice appears to be widely used in the landscape industry where the heaviest thing on the trailer might be a walk behind or a ZTR, which is okay for these things, but not okay for a tractor. Trailer's using this construction feature tend to fold up right here after a while. My trailer has 4" channel iron in the bed and the tongue and the tongue is seam welded to the bed frame back to the front axle.
Legal note: Federal Laws supersede State Laws on the same topic, including trailering. Either law really only comes in to play if you have an accident and somebody notices you have a trailer attached and they look under it for brakes to count how many were installed and were they in working order. Neither law applies to whether you can build and sell a trailer with or without brakes they are built and sold every day both ways, it only matters when something happens.
Someone said it earlier driving slow is a great idea.
Sounds like you are headed in the right direction, good luck, ric