1) most of the HOB refugiums have a minor pump to supply water to it and the overflow flows back into the tank.
2) no, the skimmer for the main tank will also skimm this.
3) this is where i start to have problems with what a refugium is for.

i will play nice though. the object is to have the
macro algae uptake the nutrients that the nuisance algae would need first. when the algae get big this is the export part of what the refugium does. the object is to just toss the overgrowth. if you feed it back to the tank than you are putting the bound nutrients back into the system. i feel pods are best bred in a seperate system. their requirements go completely opposite to what most people want done in the display tank.
see, look, i can play nice when it comes to refugiums.
G~