Being new to M-L'ing I would go right to loose powder. Just get a powder measure, not hard at all. Shooting loose is cheaper, you can adjust your loads however you want & loose is easier to ignite.
You could just use regular Pyrodex or 777, though I still would use the B209 if your gun can handle it, reliably. Just be sure and clean your gun well after shooting it.
You can also shoot cheaper bullet/sabot combinations while getting familiar with your gun. I shoot pistol bullets matched to a proper sabot often. I do a final sight in & test with hunting bullets before the hunt.