Pulling with a JKU, it's a bit of a mixed bag. Some go big, others not-so-much. I'm int he latter camp as I will be traveling with my family (wife + 2 kids) and didn't want to overload too badly. It's an overland support trailer to carry tentage, fuel, water, etc.
I opted for a smaller "jeep trailer" and got a M100 (kissing cousin to the M417) for $650. It was in OK shape - mechanically sound, some rusty spots, but not much cancerous rust that need a lot of TLC. For the $500-$1000 price point this is about typical, you start finding excellent shape or even fully restored examples at the $1500-$2500 range.
Some opt for larger trailers like the M101, but those are intended to be pulled behind larger tactical vehicles and won't leave much room for cargo capacity before you max your safe tow rating.
My trailer weighs #500 and has a capacity of #500 - I only plan to carry camping gear, not a roof-top tent or anything terribly heavy, but the cargo capacity is the dynamic weight (trailering while traveling) and can certainly hold more in a static setting. It's light enough that I can move it around easily unhooked and can even tip it on it's side or flip it on its back to perform maintenance.
Some folks upgrade the axles to heavier duty 3500 dexter axles, or match the hubs to their wheel so they can share a spare. I did neither.
All I did was inspect and repack the hubs, inspect the park brake (I don't have or really need an electric brake) and clean it up a lot.
I kept the landing leg and the lights were already 12v, so I'm just rewiring them with fresh wires and connectors. I kept the ring lunette and just got a 2" shank pintle for some axis of movement, but some convert to a ball hitch or go with a multi-axis hitch.
This is a good reference:
Trailers
If you want more of a DIY, Dinoot makes excellent kits (I almost went that route) that can go on store-bought, custom, or provided-by-them trailer frames with all sorts of options.
Jeep Trailer Dinoot Durable Lightweight Fiberglass Trailers.
Good luck - do your homework and let me know if you have any follow-up questions.