This is Turtle.

Full boxes are not a problem now a days with the piggy Back breakers
and can run
two circuits off one slot now a days.

TURTLE

Good thinking. I've got a few in my present breaker box and hadn't
thought of it. Now, back to my OP.......I need advise on what to do
about a conduit......metal or PVC? Also, what would be a good way to
connect it to the concrete block wall?