How long can homemade manicotti be frozen? I would like to make it now and serve it mid-October.?

As long as it is wrapped well I see no reason why it will not last that long.

If it is going to be baked do not put the cheese on the top first put the cheese on when you bake it. Cheese can become a bit dry and the texture will change if frozen.

If you are using a white sauce it may split when you thaw and bake just stir it a bit and it should be fine.

If you are suing a soft cheese like ricotta that also may split so I would suggest holding off on a ricotta stuffed one. Unless you par bake it first then freeze. That way any eggs will set and will help the cheese to hold together when baking again.

If you are using a red sauce do not allow aluminum foil come in contact with the sauce wrap in plastic first then in foil if you use foil. (The acid in the red sauce will eat away at the foil causing holes and the aluminum to get into the food.)

Thank you for great detailed answer. Much appreciated!