Will wearing a facemask while on a Ouija Board protect us from malevolent daemons and spirits?

They probably won't be able to recognize you with a mask on, so you'll be safe. Just to be sure, wear a wig and maybe some dark sunglasses.

Only if you hang a garlic around your neck

I can't see a face mask being much protection against a satanic being, but what I have found to be useful when playing with The Board is to get Mavis to wear her knickers on her head. I don't know if people looking ridiculous repel demons or if the thought of an old biddy without panties is terrifying even to Lucifer, but since we have been doing that we have not had one iota of bother from any sort of malevolent spirit whatsoever. 

Probably not but it will protect you from anyone compiling a "Silly Persons" list by making it hard to identify you.

Most likely not if you believe in malevolent daemons and spirits.

Only the Bible can protect you.