not a good idea. if you are going to have a crayfish (lobsters are salt water)
it has to be the only bottom feeder in the tank. it will eat the other bottom feeder or it will get eaten because when they moult they are very soft and volnurable sp to any fish.
another reason why its not a good idea is because gouramis have those "feelers" and are easy to snatch by a crayfish. depending on the species some are very agressive. the one that i had CRUSHED 2 feeders i put in the tank with its claws. to show you what i mean by moulting ill show you a picture of mines when it moulted:
and heres the agressive cray i talked about: