The only problem is the panel is recessed inside the wall.

My questions are

A) the best way to go about running the wire

B) the appropriate type of bushing/connector/fitting to go in the knockout (I can't see how to put a cable clamp in)

C) how should I secure the wire (can staple inside the wall)

It will be a run about 3 feet long running from the panel to switch box (Likely metal)