I got some chateo from two different places and they "look" clean. I was thinking about throwing it in the sump but I am still deciding if it is a good idea.Ah! Right, you want both ammonia and no2 to hit 0 within 24 hours. Normally I just ignore NO2 for two weeks until the end because that is pretty quick to go down as well. No2 usually takes care of itself in the right time period.
In terms of more biodiversity, it's less about the bacteria, and more about things like pods and algae, and then eventually some equilibrium between resources used vs. replenished (dosing/water changes/etc).
I'd look into getting something like AquaBiomics live reef rubble https://aquabiomics.com/product/live-reef-rubble which will seed your tank with some pods etc. They test every batch to make sure there's no pests/disease. You can also try seeding from someone else's established tank, but it's not as "For sure" in terms of being free of pests. Ultimately, pests will most likely make their way in, but in a nicely established tank, they shouldn't be too difficult to manage and live with easily.
Also, that's a nice product. But sadly it's OOS. Maybe there is an alternative.