To find the dose range for herbs, you can refer to the monographs in the Materia Medica or Wild Medicinals sections in the course books. If a herb that you wish to use in your formulas is not included in these classes then you can do some searching on the internet for monographs, by typing the herb name (preferably in Latin) followed by ‘monograph’. Some good sources are the American Botanical Council, the American Herbalist Guild, Herb Rally, or Rosalee de la Foret’s website. What you are looking for is a reliable source that is Herbal and clinical.
In terms of combining herbs there can be some synergising or potentiating affects when combining for sure, and often the dose that I chose starts low and may increase over time when I’m actually working with someone, because the other consideration is that every person is different. Some folks are very sensitive to their herbs and results are achieved with low doses, and others need hefty doses (one way you might discern this is by knowing how they respond to other medications, foods etc.) It is all in practice and doing that we start to learn.
You can also take a look at some of the formulas in the Therapeutics section of the course to get a feel for doses in formulas. One other item to consider when dosing is the strength of the medicine, is the plant fresh or dry (for teas), what is the ratio (if it is a tincture). Most of the dosing in the monographs and therapeutics are dry herb and 1:3 ratio.
Also remember that this assignment is a theoretical case study and an opportunity for you to practice making formulas, preparations and diet and lifestyle advice, and have someone review and provide feedback.
I hope this helps to get you on your way with dosing in your assignment.