What do you have for shotguns now?
Basically anything will work and most any shells will work. Are there things that can gain you some yards, for sure, but not really needed.
30" is long but it would probably pattern great!.
I would probably use the 870, but either would be good turkey guns. Only thing that really matters is that there finish isnt' shiny. I could care less if I grab my black shot gun or my camo. Movement is what will get you caught. The sights as long as you can see them and they hit where your aiming do not matter. I do have a red dot sight on my little youth 20 gauge, but that was set up for youth hunts as a hope to keep them from peeking. The one thing sights can help with is when we run super tight chokes on turkey guns and at 20 yards the pattern is SUPER tight. A more rifle like aiming system can help with super tight patterns close. But again as long as you can shoot what you have to point of aim you are good. I shot one bird with Grand pas old single shot 16 gauge last year, no rear sight not front sight.(once is enough though!)
I run Sumtoy. He is a great guy, call him up tell him what you plan on shooting for shells the gun ect and his recommendation will probably shoot great. If not he will switch it out for you.
Do you have some? If so go pattern them and they might do everything you want