Its pretty simple.
Pi4 HDMI to AVR. AVR HDMI to projector
Pi4 USB3 to SSD enclosure
Pi4 USB2 to 2.5" enclosure (5400rpm drive)
PI4 RJ45 to my network
I have the boot partition on the Micro SD card but the OS on the SSD; that was required when I set this up. Now you can boot directly off a USB connected SSD so no need for a Micro SD at all.
I don't use any hubs but if you wanted to connect several 2.5" spinning drives a USB3 *powered* hub might be helpful to feed the enclosures. If you go for 3.5" drives each enclosure probably requires its own power supply anyway so it wouldn't put a load on the USB.