1/4/5. We are not actually sure if USB tethering speed will depend on what type of cable and port you are using.
Based on our observation on our side, spacedesk performance (in USB tethering connection) is the same regardless of USB cable type and port.
We also don’t know if the network speed can be increased, we always get 425 Mbps speed on our side.
And even if we manage to increase the speed, spacedesk only supports 30-60 fps fixed in the settings.
2. This seems to be a Windows behavior.
There are some suggestions here that you might want to try:
3. It’s not yet finalized, but the Viewer Pro version will probably include some performance improvement/feature e.g. hardware accelerated image encoding, native USB cable connection support.