Nice another 16 year old in the forum

That makes you and me

If only my parents ran an aquatic shop.. Ohh the possibilities...
If you can get the space, try for a 75G. Considering your parents probably keep fish as well, you should have plenty of space.
with that 75, you can put in a wider variety of tangs.
I prefer Multies but its really up to the individual who keeps the fish. Brevis are less active IME.
You could probably ask your parents to bring in the shellies
If you do have that option, try breeding a more uncommon type of shellie so you can sell em at the store. Speciosus are nice and feisty