With midi over usb, you’re probably not going to run into any issues (especially if you use a usb3 hub), but, it is possible to hit the upper limit of bandwidth that a system’s usb infrastructure can support.
I hit that point in 2009 on a Linux system by trying to stream and process video from 4 or 6 webcams at the same time. Theoretically, streaming video should be way more data than usb midi though.
I don’t have any particularly good insight re: hubs and power other than that you’ll probably want to keep the topology flat (i.e. plug hubs directly into the computer, not into other hubs).
Sounds like a fun project