If you have a large tank, 75 and up... I'd say it wouldn't be a problem. Clowns tend to stay in one area...if you have the setup (lighting) then you may even want to get an anemone for the clown which will definitely keep it on one place for most of the time. As for the tangs... I have a yellow and I just got a blue HIPPO tang today. I am hoping there will be no problems when I introduce after quarantine. But I would suggest introduction at the same time for the tangs. Yellows are pretty docile, after they get settled, but can harrass newcomers for a little. That's what mine does for like the first day...then she pretty much ignores them...and even "plays" with a couple. Keep in mind that you need to put as much thought into the fish you keep as your equipment and setup. Fish Only, Fish and Inverts and Reef require very different budgets and tank setups. Figure out where you want to end up first, then plot out the steps to get there... Read a couple of books too...
125 gal mixed REEF