I added a pair of P Clowns as my first fish - but I cycled my tank first using raw shrimp from the butcher and a few pieces of LR
from the LFS
. If the tank is cycled, you can add them first with no problems. If you add damsels, and then want to add other fish down the road, it can be difficult to catch damsels without tearing up the tank.
You can setup a refugium. Are you planning a sump for the tank or just a HOB
refugium? You want to grow MACRO algae, not micro. I grow chaeto in mine and it works like a champ - my nitrates have never been detectable.
As far as tangs, there are species that are suitable for tanks of less than 100 gallons. Most species do need quite a bit of room as they get big and are active fish. With a 150, you will be fine to house several varieties of Tangs, and probably will be fine with mixing a few different species in the tank. Just research and plan ahead - don't go to the LFS
and buy fish, and THEN research their temperament, requirements, etc.