An unfinished basement must have at least ONE receptacle in it and it must be GFCI protected. If the furnace/heatpump/airconditioner is located there, there must be a receptacle within 25 feet of it (it can be the ONE mentioned above).

Bringing the circuit down the inside of the block wall, will the wire 12/2 need to be in conduit? If so, is PVC acceptable or does it need to be thinwall?

Conduit is not mandatory. As long as you're not in an area subject to physical damage you can surface mount the NM.

If you do need protection from physical damage you can use Sched 80 PVC (as well as the metal conduits).

I agree with Ronnatalie, except in certain locations (like Chicago) where the local rules require conduit. Check your local regulations.