Most of this patterning stuff is "high voodoo" and equally useful.
As MD pointed out, what you need to do is see if the shot hits where you're looking. If I get a new shotgun, I do this at about 10 yards.
To adjust point of impact, you need to adjust the "back sight," which is your eye. So you should have an adjustable comb.
As for degree of choke, use Skeet of IC for upland game or within 35 yards and Modified for everything after that, including 16-yard trap. Only waterfowl, turkeys, and handicap trap require more choke.
There is a lot of Voodoo about the brand and shape of chokes. The only thing that matters is the ID of the choke compared with the ID of the shotgun barrel (which, as MD noted, is deliberately made to different dimensions by trhe manufacturers). So I use the chokes that come with the gun.
Counting holes? Fuggedaboudit!
