I think it's always best to start low and if there is significant enough interest from a demographic that's not really represented in those buyer personas, we might want to add them, especially if they're sales are growing.
Theres no one size fits all for this question - 2 buyer personas can be perfectly fine.
Talked to the founder of DTC sunscreen company yesterday - there personas are literally "skincare nerd" or "non skincare nerd"
0-100K month = 1?
100k - 300k = +2
300k - 800k = X ?
counting "Persona" seems a bit difficult, but ANGLES is something that can multiply to infinity (I guess?)