Imo:
level 300 should have at least 3 damage preys as RP ED MS / Ek should have Dodge instead of one of them. Ofc more charms better efficiency. But not many ppl can force yourself to do bestiary.
For example I'm on level 530 Rp got only 4 charms.
but from level 200-250 you start team hunting so at least you should have 2 to improve exp with your friends. Cuz monsters there are worth setting charms on them.
Also keep in mind If you are into bestiary don't make hard ones first. As I know best calculate is by killing monsters with 500 kill count.
Nowadays while people hunting on Lava Lurkers from level 100-250 I would say you might have only one charm there. But Issavi come to Tibia with Sphinxs and Crypt Wardens so that's why you would need 2 of them. Also spectres for Blue and Red you need 1 charm but on Green one you have 2 type of monsters so it would be good own 2 charms there.