Yes that's the standard, to remove the CO2 nut. The filling rig will screw straight on to the bottle valve. This is the case a live events and robot wars.

The dump can be anywhere in the system as long as all pressure is vented from the system, usually we will close the bottle first to save gas. But sometimes this isn't possible for safety and we will vent the whole system including the main tank. I would put it after the reg, not knowing what reg you are using, it will always allow downstream so it will still vent the system.