Towing... 4 to 7 pin w/brake controller for electric brakes?

There is no vehicle built that you can drain, or vacuum, "all" the coolant out of.

The HSD cooling system lowest point is, from memory, the transaxle coolant drain. But be careful and make sure you get the correct plug, or you will be walking (Ubering??) to the parts house for some ATF

If you refilled with premixed Toyota coolant, you did better than 99% of folks, so very well indeed.

 

If you're only towing a max of 500lbs, don't worry about trailer brakes. I'm in a similar situation as you actually so I can speak well to this. My 05 tows a small harbor freight trailer and a 300lb motorcycle regularly. I've towed the motorcycle from GA>NY mountains and back. I'm doing another trip this summer with a different motorcycle to Denver, and anticipate towing the bike into the mountains a few times when I don't want to ride it in.

A month after towing the motorcycle to NY, my coolant inverter pump died. I replaced it myself and it's gone on 2 years now with no hiccups at all. I would have an extra inverter pump on hand and the tools to replace it if yours hasn't failed already. Unsure if my pump died due to the trailer, but it's a common failure point so it'd be handy to have one close by.

I've never experienced problems braking, but the car can struggle to run at highway speeds. On my 2,000 mile trip to NY, I ran up and down mountains at 80MPH. Probably going to keep it closer to 70MPH on average from hereon out with the fully loaded vehicle. It handled totally fine, but I think my engine wasn't so happy.

For my trip this summer I am going to replace/upgrade the struts & put in stronger springs in the rear to accommodate the trailer and the weight of a loaded car. Your new struts will probably be fine, but keep an eye and consider upgrading the rear springs. I hate dealing with trailer electronics so I had my towing equipment installed by U-Haul who didn't blink twice. The wiring equipment has help up fine and I've been happy with the experience. 187k miles and going strong.