First thing I can tell you for sure is you want a remote switch, at least 10 feet longer than the tail of the trailer, helps a lot when You're loading by yourself, and can't be beat for keeping a hand on the steering wheel of the car you're loading. Second, you will need at least a 2000#, preferable 4000#, and make sure you have a snatch block, it will not only double the force you have to pull with, it comes in real handy when unloading too.
Remember, you don't need as much pull to drag a machine onto a trailer as you need to lift the object.
With regard to wiring, if you're planning to put a battery on the trailer, real handy for dragging the trailer to the truck to hook up, the #6 cable you now have will work fine. If you don't have a bat at the trailer, figure on at least 1/0 welding cable, winches suck a lot of power. Also, you need to remember the ground side of the circuit. The contact you get thru the hitch is sufficient, most of the time, but when you really need winch power, it will let you down.
Finally, if you live anywhere like New York, where we have a corrosive atmousphere, use grease on all connections, and spray silicone onto the switch. I've replaced the solonoids on mine because of corrosion. Always use a blanket over the cable when pulling, and NEVER use the winch as a tie down device for the load.