I am planning to make at least a double recipe for a party on Tuesday evening. How much of this can I make ahead?

You can make the meat 3-4 days ahead. This is a very labor intensive dish. You also can boil the pasta a couple of days ahead of cooking. make sure to dress the pasta in lots of melted butter and high-quality grated romano cheese. I add cinnamon and a dash of cloves to the meat mixture. Sumac is good but Greeks always add those
two spices!

TheRunawaySpoon (or anyone else), after freezing this, do you put it in the fridge the day before you want to cook it, or put it on the oven directly from the freezer? Thanks for the help!

Sunday to Tuesday - should be fine. Wrap it tightly in plastic, and obviously increase the cooking time.

TheRunawaySpoon - I can keep it in the fridge from Sunday then, with the topping, cheese and all? That would be just great!!

I cooked this for our Oscar party and made all but the béchamel topping. The day before. I wrapped it well and put in fridge. It was fine. And our guests loved it.

It will keep assembled, but not baked, in the fridge for two days. It freezes beautifully, wrapped tightly in plastic, then in foil.