Hello

I would recommed the following

split flaps;simpler than fowler and most seen at STOL a/c like the Pilatus Porter, Husky, etc.

about the flaps area it depends on how much lift coefficient you want, flaperon is not a bad idea when STOL abilities are needed, and 30° to 40° would be fine, flaperon can also be replaced with camber-changing ailerons if you want to fly with ailerons only.

Regards, Roderick