when it comes to anything wild, im not adventurous enough to try it lol. for the co2 levels, start slow and slowly increase the amount of co2 you dissolve weekly, If you notice your fish breathing heavily and isnt as active then remove a bottle or move the diffuser closer to the surface, since the amount varies on how much plants you have. I had 2 bottles when i did my 15 gal, but it was heavily planted, i had pretty strong flow, and very minimal fish, mostly shrimps.
As far as having an airstone at night, the only time i tried using one i ended up killing some shrimps from blasting the o2 from a super strong bubbler and raised the ph within a very short time. A lot of guys here just keep it on 24/7 but at a lower diffusion rate to keep everything stable.
if you're not sure of how much nutrient your gravel has, you can always go the moss scape route. They dont require much nutrient, co2, or light. Some people has had amazing results from using just moss alone. Im currently going this route in my temp tank to raise shrimps since im using just plain gravel and im having great growth from just tap water.