You definetly dont need anything bigger than a #2 shot. As a matter of fact, most hunters probably use #5 shot. I also wouldnt recommend #2 shot anyway. Also, a big no on steel shot. For turkeys, its lead/copper, or a heavier-than-lead type shot, most commonly is Hevi-Shot. Hevi-Shot is a little more expensive, but it gives you the benefit of dropping down a shot size, therefore throwing a ton more bb's out, but still have just as much or more knockdown power. I would say when it comes to Hevi-Shot, #6 is probably the most popular. Do you need Hevi-Shot? Of course not. Many, many hunters still use regular turkey loads with nothin but great success.
If you are starting off and have a modified choke like you said, I would recommend a #5 shot and stay within 25 yards max. Back when I used a single shot 12ga w/modified choke, I stuck to that rule and never missed a bird.
The key is to practice. Find out how your gun shoots with different loads at different yardages. No better way than practicing with it.
As far as where to set up..it all depends on the land, and most importantly where they roost or go after fly down. Best thing to do is scout. Find out where the turkeys are. Look for feathers, tracks, droppings..etc. This atleast tells you that turkeys are here.
If you find out they do roost on your property, find out a general location where they roost, and that will make your morning hunts much easier. Sometimes its not that easy though. For example, for some reason, the turkeys dont roost on my property, but do travel on it. This definetly alters my game plan. Being that im used to it, I have a pretty good idea what the turkeys do and where they go during the day. This information gives me the best ideas on when and where to set up.
So again...SCOUT.
As far as calls go, try going to a sporting goods store that has them all laid out so you can try them out. When i started, I learned a slate call the easiest. You can get a decent sounding call for $20. Practice with it. Watch YouTube videos on how to use different calls, those will help.
And the most important bit of advice I can give you, being that you are a new turkey hunter..get ready for this...
PATIENCE!!!!!!!!!!
Patience is THE best tool you can have.
These are just a few things to help you out, you will learn MUCH MUCH more from ol' Tom himself, the actual teacher.
Good luck to you and let us all know if you have any questions.