UPDATE:

I finally bought a dock substantially identical to the https://www.amazon.com/VAVA-Docking-Station-Ethernet-Charging/dp/B086DS5Q6K and upgraded (thanks to a tip from /u/phurley97) the laptop to the beta bios with USB4 support. Achieved nearly all my objectives.

I was wrong about my monitor being 4K, it's 3440x1440 and the dock delivers native resolution via USB-C at 100Hz. Use an HDMI cable from the dock to the main monitor's HDMI input.

The dock I actually bought is this one: https://www.amazon.com/dp/B09QSZZL83 at about $80 -- quite a bit cheaper because everyone's just rebranding Chinese stuff anyway and putting their own logos on it etc.. Comes with a pretty big 96w power brick and delivers enough power to the laptop to run pretty well. Just enough USB ports for the different peripherals I wanted (external keyboard, touchpad, etc.) and fast Ethernet.

If I really need to get 144GHz refresh rate and/or ideal graphics performance from the GPU I can resort to a direct HDMI connection to the appropriate port. Day to day, as someone who doesn't game much, this all works fine.

I'd recommend this as a reasonably priced solution that's probably more than adequate for most users-- but do upgrade the BIOS, there was some flakiness on display detection that went away when I did.