I can install a trailer hitch and wiring on whatever CX90 trim you like for about $600. Same goes for most SUV's.
If you're not in the South Shore area of MA then you could probably find another quality hitch installer in your area.
The wiring kit is literally just plug and play ...although you do need to take the interior apart to get to the socket.
CL3 Trailer Hitch CX90
Trailer Wiring CX90
You can usually add the hitch thru the dealer as well. Sometimes they do it in house ... sometimes they bring it to me.
I can install a hitch and wiring harness no problem. I have done that previously on two other SUV's and I don't need a brake controller, the boat I am towing is only 4k pounds and a SUV will have no problem stopping it.
However, there are some people talking about transmission coolers, which is fairly common with SUV tow packages. Neither of my wife's previous SUV's needed them, but it is pretty normal for your basic unibody suv to need a transmission cooler installed for towing.
www.cx90forum.com
All modern vehicles have a transmission cooler. The tow package doesn't add anything to the tranny.
What your link references is an additional "sub" radiator that allows more engine coolant capacity.
The transmission would perform the same with or without the tow package.
Now if your are in 105d Arizona sun, towing 5k lbs uphill for 2 hours with the A/C on full blast, ... yes, there is a good chance the motor will overheat.
Also, any trailer over 3500 lbs should have brakes (it's the law). A 4000lb boat (+800 lb boat trailer?) should have a tandem axle with a hydraulic surge brake system. No brake controller needed.
I wouldn't rely on the suv brakes to stop that load in an emergency.