I don't think there is a right or wrong track. Ask 10 people how to make clams casino, and you'll probably get 10 different answers. As long as you have clams and bacon, you're OK. Your ingredients look fine if that is what you like. I don't think tomatoes are commonly used. You could go either way on the bell peppers - red or green would both be OK. I personally would not use ricotta or any other heavy sort of cheese.
If it was me, I would top it like this:
Fresh clams (I just can't do the canned clams any more)
Onions lightly sauteed in butter, Worcestershire, and Tabasco (maybe)
Bacon (I cut the raw slices into 1" strips or so) par-cook as needed
Chopped flat leaf parsley, post bake