I agree with brushhippie
I like 24 grains of Pyrodex P in my 51 Navy but it is a steel frame. 20 grains should give you a low recoil accurate load. I would use a flask with a 20 grain spout. The spout is slim and easy to use to dump powder into the cylinder.
I use .375 round balls in mine and place a felt Wonder wad between the powder and ball.
Cornmeal can be messy and doesn't provide the lube that the Wonder wads do.
Enjoy your new pistol!