The reason that you add all your clownfish (that should read only 2) and of the same species is so that they will pair up. Clownfish added individually are okay provided any addition later is a much smaller juvelnile as the single fish will have turned female if left on it's own for any length of time. I would not try and mate anything to a single maroon as they are difficult to mate up later as the female would undoubtedly try and dominate and attack any other maroon added. I would seriously recommend reading up on maroons if this is your plan. Ocellaris on the other hand can be added later as they will probably mate up provided the first fish is a much larger mature fish and the addition as stated is a juvenile and much smaller.