For baking challah, I use 17 cups of flour which I believe is the minimum shiur for taking challah with a bracha. Can I then break off a piece of the raw dough and freeze it for use during the week or do I need to bake all the dough at once to be able to make the bracha?
You don’t need to bake the dough at once. Even if you put some of it away, you can still separate challah with a berachah.
See Shulchan Aruch 326.