Boy you all are conservative I had 19 fish in my new 112 gallon started with dry rock within <3 months (fully stocked at this point fish wise).
I still have the same fish, save the Flame Angel which was recently caught and eaten by our Ritteri anemone :-(.
I guess my point is, there isn't a solid rule of thumb IMO but agree you should not be adding more until the tank is ready and if you don't know if the tank is ready then more time is better.
Should have said we did loose two fish along the way both within a very short period and to Brandon's point that is the purpose of QT. One wasn't healthy in the first place and didn't make it over night. The other was injured at LFS when netting and we didn't catch. Most of mine do go thru a seperate aclimaation tank observation but not a QT
the hobby is simply vastly vastly trained to fear ammonia control but it's one of the most rock solid, inherent and unwaivering aspects of reef tanking. such that I don't test for it, and I don't ever need anyone to test for it to manage their tanks remotely. it's such a given, that's the angle I operate from
technically all the ATM Tanked show tanks were massive initial stocks on day one. skip cycling works, it's easy, sellers use it and employ it like the force at marine trade shows etc where full complete tanks are due by friday
only the buyers get the opposite info: your cycle might not be done/safe/ready/not starved, so buy this items to reinforce so you'll have ammonia peace of mind
I do agree bottle bac is a big deal in managing big initial bioloads long before surfaces had time to independently take on bac.
I on my behalf, I recommend one at a time or No more than two. Reason is - the Addition of fish increases the bioload on the tank and adding them periodically allows denitrifying bacteria to keep up with new bioload as tank matures