Just echoing what cmor said. I use the exact same setup (10g, PVC
elbows, heater, biowheel) but don't use any additional powerhead.
The reason you don't want substrate is in case you have to use medications. Any type of substrate or live rock can interfere with the medications. For example, sand/rock will suck copper out of your tank quicker than it can do any good. But like cmor, I don't medicate the QT unless there is an obvious reason to.
When I quarantined by clown goby, I bought one of those fake plastic acropora corals to make him feel more at home. He seemed to prefer it over the PVC