I'm wondering- the boards (not the cardboard separator plates, but the thicker boards that go under the whole cake and many people edge with ribbons)... do you charge for that? is it a deposit? do you get them back? or is the cost factored into the cost of your cakes?

Those are called cake drums. They are usually made from thicker layers of cardboard or of foamcore and are wrapped in food-safe foil. They are considered disposable. The cost of the board should be considered when calculating the cost of the cake.

Thanks! I was thinking of having my husband make some out of MDF- but then it wouldn't really be disposable.

If you have them made out of MDF, then they're cake stands and you should charge a deposit = to the replacement cost (I'd include the time it takes your hubby to make them in that cost) and then refund a portion of the deposit upon return (basically the deposit minus however much you want to charge for the rent, or you can refund the entire deposit and include the "rent" in the cake price).

Are the cake drums really strong enough to hold a heavy cake? If I do a 14, 10 and 8" - is the 16" cake drum strong enough to hold that much cake?

Absolutely, drums are strong enough. I use them exclusively.

You are all amazing resources- thanks!