Yes, You can freeze the sauce for later use. I usually cut the recipe in half and I still have enough leftovers to freeze. I'm sure that ground turkey can be substituted for anything that calls for ground beef although I haven't tried it.
Also I have thrown other stuff into the sauce to make it my own (Mom hates it when I do that!) Mushrooms, olives, or anything else that I think sounds good at the time.
experiment and have fun!
Toni :)