How to prepare tank for large fish addition?

[Halal Hotdog]

@Halal Hotdog
I have 2 anthias, 2 chromis, 2 clowns, 1 mandarin, one chocolate tang, one convict tang, and a one spot foxface whose my biggest fish at maybe 3 inches. Adding a 5 inch CBB, a tomini tang, 2 blennies, a wrasse and 6-8 more small chromis

*short term tank for these tangs*

This is a recipe for a disaster. The tangs and foxface require more room than a 90 gallon can provide. In saltwater size is usually secondary to type of fish. A lionfish larger than any of your current ones could do fine in your system. A small sohal would not do well. If you know you are going to upgrade, then why not just wait until the tank is ready then add fish?