I was wondering if anyone would know if above stove microwave venting
is a standard location and size for microwaves?

Probably..IIRC ours (Kitchenaid) is 3 1/4" X 10" thru the wall..they can
also go up thru the cabinet.
Pick a brand like Whirlpool and/or GE , go to their website and look for
schematics to download