My experience with the no tripods rule is that it is there but not always enforced, as long as your tripod is not so big that it would block the path of others or cause them to trip over.
As for the no flash rule, this is always enforced in all museums, so always bring a f/2.8 or better lens to such a place.
My gorillapod was ok
Again make sure that u dun cause any inconvenience.
Ryan