a banana chopper will work fine for both right and left wing feathers.
for me, li'l choppers work best reversed - that is, i prefer a right wing chopper for left wing feathers.
as to feather shape, only you can decide what will work best for .... you.
i have more than a few choppers, including the german vario, but mostly use a li'l chopper big banana that i adjust for a shorter and lower feather. all my arrows sport 4-fletch bananas that are either 4" x 7/16" or 4-1/2" x 5/8". to each their own, a great aspect of making yer own trad gear.