Welcome to the community. Usually as a general rule of thumb we say one fish per every 5 gallons of water. Obviously depending on their full grown size. If you plan on up grading in a couple years take that into consideration too. That being said I'm my opinion you are definitely not over stocked. The Tangs should be fine. As someone else said they could show aggression towards one another but most likely not as they were put into a new tank around or at the same time. That's the biggest thing with keeping multiple Tangs. You certainly can, you just want to introduce them at the same time so neither establishes the tank as it's part of the Reef and for extra success buying them small will only help. I like someone else's suggestion for a wrasse. They are beautiful and very personality having fish. Take a look at a Leopard Wrasse; one of my favorites!
Welcome to R2R and the wonderful folks, information and help.
Patience, it is the big word around here, Reefing is patience to cycle, to watch things grow, to keep your tank balanced.
I recommend to everyone joining to create a tank build thread.
1. You get to see where you have started and how much you have grown in this hobby.
2. We love pictures and to see what your doing with your tank.
3. It’s a great learning tool for all of us to see what works and doesn’t . We learn great stuff from each other.
Lastly the only bad question here is the one not asked...