How much weight is mostly a function of what I can fit in it but I think 2 ton would be adequate. It would be pulled at a speed of no more than 5mph. Terrain is hilly and bumpy.
I went and bought one of those trailer kits for a 5200lb single axle together with some dump trailer plans as I don't really have any spare bits lying around other than the wheels and a set of trailer lights.
I have been looking at some scissors lift hoists on Ebay and Pierce Arrow. The logic generally seems to be that a scissors lift works much better than a single cylinder although the single cylinder is less expensive and probably adequate for my needs. One thing that's a little unclear from looking at pictures is how a single cylinder setup needs to be mounted. I would think it needs to be mounted at a shallow angle to the bed. Also, not sure how the pivots at the end of the bed are best made - I should probably go to a trailer dealer and take photos.
My plan would be to run the hydraulics directly from the tractor rear remote as this would save the need to put in a valve, pump, motor, battery, etc. I figure that even if I use something else to pull the trailer in place, I can plug it into the tractor to dump.
Hopefully I wont get a shock when I price some steel.