I'm making a recipe that calls for sweet chocolate. If I have semi-sweet, do I just need to add sugar to taste or also add butter or cream?

I would use the semi-sweet chocolate and not worry about adding more sugar. You will have a slightly less-sweet result, but that iusually sn't a problem since so many recipes are over-sweetened.

It depends on the recipe,really...If the texture is not important you don't need to add cream,but if you must,I would go with it.