So I ended up doing two chains, one with comet and one with acetone. This is after the initial degreasing step, so I still used mineral spirits there for both of them.
My understanding is that the last step is meant to remove any film that gets left by the degreaser, so the wax can adhere to the chain better.
The video I shared is for paint prep, but it makes the claim that the standard acetone/alcohol approach actually does leave a thin film whereas comet/ajax/bar keepers friend rinsed away with water can eliminate it completely.
For my chain with comet, what I ended up doing was a very brief hand scrub with water + comet. Then I put it into a ziplock with more comet and a little water, and I put that ziplock into the ultrasonic cleaner (with water in the ultrasonic cleaner). After that I took the chain out of the baggy, rinsed out the chain in water, and threw it back into the ultrasonic with only water to try and make sure all the comet was out. I let the chain dry and I didn’t see any white from left over comet, but obviously can’t see into the rollers.
Not really sure how to compare the results, but I’ll keep track of mileage and see if there’s any noticeable difference.
For my wax I used Runaway Bike PTFE Powder from amazon and a 1lb paraffin block from home depot (https://www.homedepot.com/p/Household-Paraffin-Wax-BW-407/314269840). I did ~1:75 ptfe:wax by weight.