If your sweet potatoes are not paper thin, you will need to increase the baking time in order for them to become tender (and cover for half of the total baking time).
This lasagna is not very tall after it bakes since the vegetables cook down a bit. This recipe yields 4 large servings for us (or 6 smaller servings). To bulk this up and increase the number of servings, you could add 2 layers of regular lasagna noodles in addition to the sweet potato layers.