You can cycle with fish, or by using ammonia (fishless). Fishless is safer for the fish involved in the process, and will get your tank fully cycled quicker. Cycling with fish is OK as long as you take things SLOWLY.
If you decide to cycle with fish, then it's safe to start now, with only a FEW fish. Dont plan on adding any more for at least 2 weeks, and then only if the water tests OK and the existing fish are healthy.