1. I plan on mostly shooting clay pigeons. Is the modified choke suitable for this?
2. Even though three of the chokes are approved for steel shot, is it still best to avoid steel shot to reduce wear-and-tear on the gun? In other words, is shooting steel shot even through approved chokes hard on the gun over time?
3. I'd mostly just like to use the modified choke, which is approved for steel shot. Is there any 12 gauge ammo (besides slugs) that I shouldn't shoot through this?
4. When you are changing chokes, what lubricant due you use? Are Remington oil and Break-Free CLP good for this?
Sorry, if these are dumb questions. I'm learning.
1) Depends on what kind of clay pigeon shooting you plan on doing. Modified is a bit tight for skeet, a bit loose for lead shot in trap and probably just right for most sporting clays. (steel shot shoots about one choke size tighter than lead, e.g. a modified choke with steel is similar to a full choke with lead)
2) If the choke is OK for steel, shoot steel whenever it is required. Don't shoot it if it's not.
3) Modified choke is OK to shoot with any load I can think of.
4) Best is anti seize, but it's messy. If you get it on your clothing it's almost impossible to get out. It's best for chokes that are going to be installed and left in for a long time. Grease is a close second and I'd use it instead of anti seize if you plan on handling the chokes a lot. Any oil is a distant third, but better than nothing.
You've posted some good beginner's questions. You should see the dumb ones.