Running an exit relay from home would be a very bad idea, and if your IP frequently changes you might not be picked as guard relay. But I don't see why you couldn't run a middle relay from home, as long as you don't have a traffic cap.
You can run an exit relay from home, at least in the US. There are some ISPs (mostly on the East coast, afaict) that may not help you, but most of them seem to understand how the laws work.