Even though I bought the tow package from the dealer up front, I still had to bring the vehicle in to have the hardware and electrical installed. YMMV.
If you have the wiring harness pre-installed, pull out the rear deck to access the spare tire. If you don't see the plug somewhere inside the compartment, they may have it tucked behind the left side panel. Facing the rear of the vehicle, pop out the left side interior panel and look for the power module and/or harness plug. All the cargo area panels comes out fairly easy. Just pull them straight back from where they attach to the body. They snap back in even easier. Some of the foam seals may have to be pulled first, so keep an eye their orientation. Some of the panels overlap, so keep an eye on which ones come out and go back in first. It's simple, but I don't want you to go in totally blind.
If you don't have the tow package electrical, honestly, I would buy them in the aftermarket and install them yourself, unless you don't feel comfortable doing any of this.
I installed the oil cooler kit myself. I don't do a lot of towing, I like neat options like this, so I installed it. It will make your coolant temp run a little warmer, but I think the intended benefits are there. It's up to you on whether or not you actually need it.