When I go to pattern my gun I always use big paper (30" x 30" min). Big paper lets you see the whole pattern, even if you happen to "pull" a shot a little, you won't waste those high dollar shells.
I set my paper up, usually at 40 yds and either put a 2" dot in the center, or tape a turkey skull & vertebrae target to it. I am not sure if you are going with a lead shells and 12ga & 2 3/4" shells or a 20ga & 3" shells, but if I were using either of those I would start at 35 yards and be pretty happy if I got a good 35 yard pattern.
If I am testing a new gun/choke/shell combo I am going to first shoot my longer range to see what the combo does. I don't need to shoot high dollar shells at 20 yds and 30 yds if the pattern is not good at the longer range. If the combo is good I will pattern at different ranges, both longer and shorter, to see what the pattern looks like (and where it hits) and at what range it falls apart.
If you are just shooting 1 choke and 1 type of shell you might start at 35 yards and then go either shorter or longer depending on how the pattern looks.
This patterning will also tell you where your gun is hitting (Point of Imapact, POI) in relation to the Point of Aim (POA). If the gun does not hit where you aim there are a few things you can try to correct this. The options are limited unless you have a gun that come with shims to adjust the stock (some Benellis have this). To see where the gun is hitting try to draw a 10 inch circle around the densest part of the pattern and the center of that circle is your POI. If the gun shoots low you need to raise the rear sight which is your eye. You can put some padding on the stock to do this. If the gun shoots high you need to lower the stock or raise the bead. Not a lot of practical options to lower a stock so you can raise the bead by putting something like a Hi-Viz magnetic bead on. If the gun shoots left or right or too much high or low to adjust, you may need to go with adjustable sights.
Once I get a pattern I will hunt with I like to see how tight the pattern is at short ranges and also at what range it no longer will cleanly kill a turkey. Keep in mind that shotgun patterns can become inadequate in a hurry once they start to fall apart. Just because a pattern looks great at 35 yards does not mean it will be good at 40 yards.
I also like to know where my gun hits when I shoot from different positions. I usually just shoot target loads for this but I do like to shoot my turkey load from the sitting/hunting position. I shoot target loads while sitting and aiming extreme right & left and from the prone position. I also practice off-handed shots but never with turkey shells.
One thing I have learned, especially on an off-handed shot, is that I am not as good as shooting from a good solid position. So I bring my max range in a bit to something I am comfortable with on a less than ideal shooting position.