awhitson Will the Pro tolerate a USB 4 port hub on any of its USB ports?
Depends.
The answer is "yes" if it is an unpowered hub (a.k.a., bus powered hub). With the caveat that the total power used by the new ports does not exceed the power available from a single Raspberry Pi port (check Google for power capability for each Raspberry Pi 4 port).
The answer is "perhaps," when it comes to powered hubs.
I went through a dozen hubs before I found one that works with the v2 ASIAIR. Some of them will cause the ASIAIR to refuse to even boot up. Some would produce drop outs sooner or later, etc. I finally found a 7-port Anker powered hub (model AH221) that is mostly reliable, and it happens to be the very first in the list of Hubs that are listed as not back-powering a Raspberry Pi:
https://elinux.org/RPi_Powered_USB_Hubs
A footnote in the above Wiki says
"7 Port USB 3.0 Hub, model AAH221. Input is a USB 3.0 type A. This hub uses an external 12V switching type power supply. It does not function as a bus powered hub. The hub does not backpower the Raspberry Pi, and appears to have complete isolation on the 5V lines between the input port and output ports. The 7th port is a BC 1.2 spec port. The manual status up to 2 A can be supplied on the charge port, when no other devices are connected."
(I.e., it needs to be powered, and may not work with only the bus power from the ASIAIR USB port.)
Amazon shows it here
https://www.amazon.com/Anker-7-Port-Adapter-Charging-iPhone/dp/B014ZQ07NE
The downside is that I have found that the Anker hub does not work well near or below 0ºC. I.e., like most consumer products, it is designed for in-home use. Try to mount it on top of something that generates heat, or inside a box that has warm equipment (in my case an ABS box at the base of my tri-pier, containing the ASIAIR and an eero mesh router). I have never tried heating resistors; it might work, the problem may be melting plastic :-).
The nice thing at least with this powered Anker hub is that it is run off the standard 5.5mm/2.1mm 12V power connector, which should be compatible with the most common connector used in the hobby astronomy world.
Chen