Barrel length if what you like, and only you can know that.
Years ago, I had the privilege of examining an original Tower Flintlock Double Barreled Shotgun, circa 1775, that had 36 inch barrels, about a 12 LOP, and a buttplate made of brass that was just short of 3 inches wide. I don't recall the overall weight. What I do recall was that the gun balanced perfectly exactly where the forward hand would hold the gun on the forestock, and that it came to my shoulder easily, and my eye was looking right down the center at the front site. I even closed my eyes and mounted the gun with my eyes closed, and then opened them to find that I was again looking down the center of the barrels at the front sight! I tried the gun to feel how well it swung, and it was just fine. Not too muzzle heavy, and not too light. It was a 12 gauge gun, and was in the private collection of a Doctor living in St. Louis. The gun has a sling swivel mounted on a ferrel in front of the forestock, and another swivel for a sling mounted to the front of the trigger guard. This we expected as its origins were military as the Tower Armory made or at least put together thousands of Brown Besses for the British Armory, and kept other weapons over the centuries it was in business.
I think you could do worse than to have a gun with 356 inch barrels. If you like them longer than that, then go for it. I am shooting a Fowler in 20 ga. that has a 30 inch barrel, and it feels fine shooting both shot, and round ball. The gun was a gift. If I had ordered it, I probably would have asked for a 36 inch barrel. I am not hunting Waterfowl, or trying to take long range shots at turkeys. The deer I see will be within 50 yds, and a 75 yd. shot would be considered long enough that I would have to have a very good reason to take it. The shorter barrel works fine for my hunting needs, as does the lighter gauge.