Aquabiomics measures the range and relative amounts of different bacteria in your system (water & film samples). You can then compare your populations to their diverse data set. I find it interesting, but cannot say I know what to do next given that information. It might distract you from some of the pain and suffering.
No, there are no rules. For me, once I have a growing sponge population, I won't hesitate to populate with expensive sticks. Until then I stay with the hardy SPS that is cheap.
There is one other thing that has not yet been mentioned. Parasitic pods (white bugs, red bugs). I had them. Mine were working from the base up. Typical dips don't kill them. Interceptor is the only known method for killing them. Not a lot of people are doing Interceptor so they are getting around the hobby. What is your wrasse population like?