For your first fish, you don't need to quarantine them if they are the only things in the tank. But keep in mind, if they do get sick and you need to treat them with copper, and you treat your main tank with copper, you will kill all your inverts and not be able to add inverts in the future. So I would still recommend quarantining them, in case you need to treat with copper.
You don't need to wait long after adding the cleaner crew, you can add fish as soon as your tank is done cycling.