Just my opinion, what I would do. (sorry about the book load here. just trying to give some good advice)
I would wait and contemplate my wish list of fish for the tank first.
Start out with a hardy fish or 2 to test. Once things are ok-
Then focus on most of the smaller fish I'd like to have. Add them slowly over weeks to months. Small individuals such as wrasse specimens, or different chromis species, a dottyback, cardinal fish, many many other small types you may like. Possibly a schooling species if you choose to do so. Just suggestions here... Allowing the smaller fish to acclimate first will give them time to develop strong territories and get really use to the tank as well as healthy feeding in it.
All while not being pestered too much by a larger fish. (Tang/other)
Then Perhaps contemplate which Tangs I like. Which ones would work in a certain adding order together and what will work over the course together in the specific tank. If I would ever want more than 1 specimen of Tang in the tank. Which should be added first, and what size approx. it should be.
Personally, Once I was ready for the Tangs. I would add them all at once or close to the same time. Keeping specimen attitudes and sizes in check with each other as much as possible. Ex: A less aggressive Tang may be best to be slightly larger than a more aggressive Tang. When they are added together. This kind of helps keep some things in balance a little. (fighting etc..) Personally I kept a Sailfin Tang, Yellow Tang and Hippo Tang all together in my last grouping. My first were the Sailfin and Hippo Tangs Close to the same size as eachother. Then the Yellow Tang which is typically but not always more aggressive was added last and at a slightly smaller size.
In end result all had occasional squabbles. But all got a long very well like 3 best friends for a few years. However, eventually the Hippo did grow to be the largest of the three. It meant nothing as far as superiority in my case. All were about equal. But I can tell you the Hippo "poops" way more than the others. It makes A LOT of waste. Eventually If you are keeping a lot of corals, you need to keep up on the water changes big time. Even in a large tank. Common sizes: 120, 150, 180, 220 - These fish depending on how many you keep and what else, produce A LOT of waste and Eat A big food bill to stay healthy.
Just my take, to be helpful in your future planning..
Big fish in a home "Reef":
Keeping this all in check with water changes and calcium replacement.. can be a concern in some systems for some people. Depending on how you want to maintain it. How often. Consider your other equipment involved and what coral types you may want to keep. Maintenance not just of the fish diet and health but especially of the water conditions of the overall reef, (for Corals) can be taxing with these big guys. If your not ready to manage a system like that. Tangs are great. But big ones can tax the system, with waste load if it is not managed correctly. If you have any SPS corals, it will be a concern to watch this and do it all right. Considering a lot of things a head of time, saves money and disappointing mistakes.
Think and be prepared to buy what equipment you will need for the long range plan of things. Adjust your set up for things before purchasing too much livestock. When you can of course. It's easy to want every coral or big fish. But one day if it outgrows the maintenance plan, you don't want it to be too much to keep up with or cause expensive fish or especially Coral loss.
Something a lot of people don't plan through right when they start out.
But when $ losses add up from poor planning some hobbyists get discouraged. So have patience and plan right.
