You should have, at a minimum, a transmission cooler. The Highlander towing package, besides the transmission cooler, includes a heavy duty radiator with a engine cooler, higher fan capacity, higher output alternator and what Toyota calls "prewired harness."
The hitch, either Toyota OEM or an after market is very easy to install. Here's a link on an after market install,
The Toyota hitch is expensive but it is higher off the ground and has that "build-in" look.
I mentioned the "prewired harness" that is part of the towing package. I would think that all Highlanders would come with the prewired harness as it makes no sense to have tow different wire harnesses in a production environment. The prewired harness is simply a connection under the driver's dash for a converter (which you will also need to get) and wires/connection near the driver's side rear end. When you get a converter, the kit also comes with another short harness that plugs into the rear wires/connection and ends at the hitch with a 4 prong trailer plug. If, in fact, your Highlander is not prewired, then it comes a major task. Look at this link to see if you have the converter plug under the driver's dash,
or look at posting #6 in the following link for a picture of the connection,
To plug into your Escape, you'll need to add two additional wires for the brake controller and for charging the trailer battery. Here's a link on how to wire a Highlander for these additional two wires and installing a Prodigy brake controller,
It looks like an overwhelming task but is really very easy to do.
I pull a 19' Escape with a 2008 Highlander without any problems. If you have any questions, just drop me a PM.