If something does go wrong, (like you set a waypoint that is heading directly for a tree) you will need to switch to stabilise (or loiter) modes to get take over control.
Very funny , but actually this will also work in a way since all modes on arducopter still have some wiggle room, when flying in auto mode you can still use your sticks to kind of nudge your platform if you want. But best to switch to stabilise/loiter/RTH modes.
The radios work on the same concept where they are paired together. You can set up the radio ID via the mission planner so you will need to make sure that this is unique to your telemetry radios if flying with someone else in the same area.