Good advice, a person absolutely has to be aware of the way a trailer will affect the dynamics of a tow vehicle. And while we're on the subject, when towing at highway speed proper distribution of weight over the trailer's axle is also crucial for safe towing. Plenty of good articles out there on the web so I won't bother repeating them here.
25ish kW is not bad for steady state load. I was pulling more than that for sustained periods when I did my test run into Manning park and I wasn't particularly heavily loaded or traveling unreasonably fast on the climbs, well within the design limits of a regular passenger car. The Bolt's power train should have no problem handling that load (in terms of cooling).
This spring I'll probably throw a receiver in the car so I don't have to take the Jetta when I go mountain biking, and it probably won't be long after until I sneak a trailer light controller in there.
Once again, good job giving this a try. I'm sure the Bolt made an excellent tow vehicle with tons of torque, all its considerable mass low down, and regenerative braking to help slow the load.