I agree a 24" to 26" would be all that is necessary and a 12 bore would work fine.
I personally would prefer a round ball gun, as a .730" (583gr.) to .740" (620gr.) ball has all the weight necessary and higher vel.
than the heavier conical- for hunting the animals you mention.
Higher velocity means flatter trajectory and a longer point blank range. This becomes important past 75yards or so.
A 5 dram (136gr/) to 7 dram (190gr.) loads will cover quite nicely and produce 300 to 500fps higher vel. than typical Paradox bulleted
loads. Will they shoot in a Paradox rifle?
I don't know the answer to that question.