I have gone with the one caliber rule on rockets that approach the subsonic <.8 range. In one case I had one flight closer to .9, so technically entering the transonic range. All of those flights were nominal.
I have not used a nosecone AV Bay above that, just more of a traditional design. Although I have some HED designs in the works that push well into the 2.5-3.3 Mach range, so at some point I will have to dig into this deeper.
As far s the number of holes, well that question has been asked and answered many times. The responses vary from a single hole, to many, but most commonly three as a min. Over the top surmised it well IMO.
I tend to line my holes up with the fins for no other reason than I like the look, which is highly subjective. This includes using three holes for a three fin rocket and four holes for a four fin rocket.
At the end of the day I do believe that this is one of those, "if you get it mostly right" then it will work, at least for most flights. I have personally never had a failure in this area with velocities up to Mach 2.4. However I have experienced inaccurate altimeter data with a mid power rocker that I retrofit a JL Altimeter Two into roughly five years ago. In that case I drilled three holes all on the same side. At that time I knew nothing about this and had zero experience.
I just fixed those holes on that rocket this summer.