Theres not a set number that is suddenly "too much". It varies greatly person to person and even in an individuals life it ebbs and flows, obviously. Some of us were taking it once or twice a week for a long time, and then had long periods of less frequent use, then maybe once a month, then etc etc. Theres apprenticing shamans in the amazon who would take it everyday for a long time, or everyday but bi-weekly, etc etc
Theres really no point in worrying about things like this... Just go with the flow and do what you feel. If it becomes more than you can integrate, slow down or take a break. If your on that part of your journey where you feel more frequent use is the right thing to do, then go for it.
<Ringworm>hehehe, it's all fun and games till someone loses an "I"