I used a tekonsha p3 in my commander. It's a proportional controller vs time delay which is much nicer. If you are ok with electronics it's not a difficult install. There are 4 wires, power, ground, brake switch trigger, and brake signal to trailer. If you have a tow package the signal to trailer is already run from the hitch plug to under the dash by the kick plate or whatever it's called. It's a green wire.. The brake switch trigger I just used one of those self tapping crimp on wire thingies (technical term). Then obviously power and ground from battery. I did however use a relay for the power wire so it would only be powered when the jeep was on..

WDH it pretty straight forward, but does need to be setup correctly, again not difficult but does take some time and measurements to get it right. I bought my trailer used, and negotiated have that in the price so I can't really comment on price anything.

As far as the trailer goes, that pretty big for XK/WK, keep in mind that the empty weight means before accessories also (generally) so no water heater, AC, batteries and whatever else.. let alone fresh water, grey water, black water, then all your crap that you are going to fill it with.

I towed a 21ft (5200lbs dry) trailer from CA to MI to DE.. it wasn't fun, but it had to be done... I had a WDH, the p3, and a friction sway controller, I had to keep speeds around 57 mph, and still only got 7.5 mpg.