What is a good substitute for goat cheese in this recipe. I thought about Feta, but that might make it too salty?

Definitely! You could make it fun with some chopped herbs, or do what I did recently with a lasagna and make a walnut sage pesto that you can stir into the cheese. Have fun with it- I've found this recipe to be endlessly adaptable having made it 20 or so times :)

I wonder if you could do mascarpone? It might have a little more tang than the ricotta.

I've used crumbled blue cheese in my lasagnas before so you could add that for extra flavor (using about 1/2 the amount of cheese called for), or just replace the goat with an equal amount of ricotta. Hope that helps!

You could try ricotta, though it won't have the same tang as goat cheese.