best not to ever QT inverts with fish, most meds that you will use on the fish will kill the inverts. You mentioned that you will not be using meds, however if you need to go Hypo Salinity, like say the fish get ick. It would be bad to only have one qt tank.
Also why would you QT crabs, unless you are waiting for the main tank to stabilize?
Usually just drip acclimate the inverts and then add them.