A few thoughts on shot sizes: when I was a kid, #4 shot was considered daringly small but as I got into the lore and science of upland shooting, authors like Burton Spiller started telling me that what mattered were shots on target, not the size of the ones that hit. A master Maine grouse hunter, he favoured shot as small as #9 when he could get it, rarely in his day (the early 1900s), but he wrote that he always used #8 if he possibly could.
Nowadays the ammo makers list shot size #6 as the most all-round choice, but Spiller adjusted me down to 7.5 for almost everything, and if I think I'm going to encounter woodcock I load #8, which OK is conventional wisdom, but it still works well on grouse, and rabbits if I want to carry one. Anyway, low brass 7.5 has always done me good service, patterns well in my favourite SxS and works on the critters I want to eat.
This is all about upland lead shot of course, steel changes everything but I would only use that on waterfowl, one federal law I can really get behind.