Huh, I didn't think anyone had ever bred common plecs in an aquarium, so I haven't seen anything about breeding them. But presuming raising them is similar to other species that have been bred...
A breeding size common plec must be seriously cramped in that tiny container. Might be better to leave them in the tank unless you're worried about them being eaten by the other fish?
Forever or until you want to sell them or move them to another tank to free up space.
Once their egg sac is gone. Should only be a couple days. Zuchinni is good, spinach, plecochips, etc. More variety the better.
I'd just add the driftwood, assuming you have room.