I'm not sure if the weight issue truly disappears with the "right gearing". For the first time ever, I've found myself walking up a few hills. Usually just my driveway, but when I had the 500 lb load on my trailer, I had to walk up the two hills between town and home. Even pulling the bike & trailer up the hill on foot was close to my limit. On my driveway, I actually parked the trailer and fetched it with my Blazer.
Anyway, I've been wondering if one might need outriggers... like training wheels to improve the balance at the very low speeds necessary for hill climbs. I could imagine going with a 40T in the rear and a 20T in the front. One could even do more extreme gearing if one put in an idler which I've considered with my fat tire bike.
The other issue I've run into on my driveway (steep paved) is traction. Even my semi-smoooth fat tire often looses traction on the driveway. My SPD bike shoes have hard soles, and they also have traction problems on the driveway. Perhaps super-low gearing or knobbies would help, but I'm at close to my limit.
My current heavyweight trailer is built on wheels with kid's bike pedal/hub brakes. So far they seem to be holding up to the abuse, however I worry about the added friction. I did repack the bearings, but they weren't designed for this use. My next generation may be pre-configured for disc brakes and through bolts, but that will also add quite a bit of expense.
However, I never got the brakes hooked up. I had originally intended to make a mechanical "surge brake" like boat trailers have, but they would also be easy enough to connect to brake levers with the right place to activate them and the right trailer disconnect. If only I had 3 hands.
The biggest question is whether the brakes are really necessary. With a 500 lb trailer, I wasn't a "speed demon", and the heavier the trailer, the slower I go. So, I think I can stop on flats. I can usually stop the bike on hills with enough distance (although stronger brakes on my bike would be nice). I have never needed to do an "emergency stop" on the couple of hills I most frequently pull my trailer over.