Well, just to be devils advocate here, lol, you technically dont "need" a cleanup crew. If you like the inverts, then sure by all means add some, BUT if you think you have to have them thats not really correct.
Keep in mind, that if the inverts are cleaning algae and stuff up they also Poop like fish do, and will contribute to the bioload of your tank.
I happen to LOVE LOVE crabs, like emeralds, so I always have them in my tanks. I also love the narcisius snails that emerge from the sandbed when you feed the tank, though they dont eat algae they are super cool too.
I have added inverts before fish, with fish and after fish. It really doesnt make a difference. Just make sure you can feed them if you dont have fish and arent feeding the tank for fish.