The Item type required for each Channel is identified next to the Channel in PaperUI.
In the above screen shot, Heartbeat and Smoke must be linked to a Switch Item. Battery Level must be linked to a Number Item.
Possibly.
Linking two Channels to one Item is a rare occurrence. This thread is the first one I’ve encountered where anyone has attempted it.
Typically one has one Channel linked to on Item. If a command sent or received on one Item needs to trigger some other device to do something, that is done through Rules.