We are so glad that you are enjoying the course and that it is adding new ideas and can also compliment your experience as an RN. This is such great news.
Your questions are great. Percentages, strength, dose and longevity safety is quite a lengthy subject and something that you will continue to learn about in further studies but there is also more focused information in text books and resources aimed toward Practitioner Herbalists. A good place to start there would be ‘Medicial Herbalism’ by David Hoffman, or ‘Principles and Practice of Phytotherapy’ by Simon Mills and Kerry Bone. There are other books looking at specific groups of herbs that review percentage, dosage, safety in length of time given etc., as well, such as ‘Herbal Antibiotics’ and ‘Herbal Antivirals’ by Stephen Harrod Buhner or ‘Adaptogens – Herbs for Strength, Stamina, and Stress Relief’ by David Winston, etc. This is a good place to start, but the above are also names that you can look up to find more articles, books and information with a bit more clinical focus (esp. both David’s, Simon and Kerry)
For your question around how long barberry could be safely taken in a UTI tea while still being effective. The tea is taken so frequently throughout the day (higher dose- 2tsp/cup, 5x/day). If this was taken for 4 days, a change will likely be seen by then and you could shift to continue the tea but without the bearberry to round off the course. The thyme is still working as an anti-microbial agent and the nettle, plantain, marshmallow leaf, horsetail to heal and sooth the tissues while still helping the body ‘flush fluids’. You could likely get away with another day or 2 with the bearberry without much trouble if you really felt like it was necessary.
Therefore the short dose including bearberry (4 days or so) then continuing on with a BPH/urinary and cardio soothing/toning supportive mix would be great. Many of the anti-microbials can be irritating to the mucous membranes and flora of the urinary tract so at some point it can be the most useful just to use the soothing, healing and toning herbs for the area. At this point you might find that the symptoms/concerns start to go away as the tissues on the urinary tract and prostate are given a chance to tone and heal up.
I like your thinking in regards to the cardiovascular support in with the BPH and/or UTI mix. Adding hawthorne is a great idea.
I hope this was of some help, it is a huge topic but also interesting to continue to learn the details about each herb and their specifics as you go along your herbal learning journey.
With warmth and care,