I highly recommend the Handbook of Medicinal Herbs by James Duke, it’s a great resource for their activities, indications and most important: recommended dosages by different organizations.

Some plants and herbs can be consumed every day, or in high amounts, without risk or toxicity (such as olive leaf). Others should be used in isolated events (with strong alkaloids, etc.). Others for some time (days or weeks, or months) but not indefinitely or in large amounts. Learning the active principles of the herb or plant in question, and which of the same family (or even different) have the same one is important. Again, great work with the research. Regards