Hello!
I also have a 90, in which I keep a humu, a niger, and a panther grouper (temporarily). I will either need to upgrade or take the grouper back...
I do not know what your experience is with tanks, but:
Once the humu and the niger are established in the tank your choices will be limmited; it is better to add the most aggressive fish last.
Since you start from scratch, you will need several weeks if not months before your tank has come to equilibrium (including the period needed to introduce each new fish etc).
In addition, depending on your filtration, LR, LS, water circulation etc, you will understand if you can keep another fish.
My advice to you is to carefully plan what you want to keep, and stick to the plan. I have had a 90g for several years, and my first attempt was a disaster. You simply cannot keep all these pretty fish that you see....
I paid dearly for my mistake (money, time, hustle, dissapoinment, and most important dead fish). Do not overstock.
There are times in which I feel that the humu and the niger are "confined" in the tank
In any case, good luck, patience, and asking questions is all you need.
