Forgot to answer the rest of your question.
Regarding yeast selection and nutrition, this is your friend: https://scottlab.com/content/files/Documents/Handbooks/WinemakingHandbook2020.pdf
There are tables there that will tell you the nutrient requirements of each yeast and detailed descriptions of their flavor profiles. There is a spreadsheet linked in TBE's paper I linked above that you can use to calculate your nutritional needs.
Assuming fermax is roughly analogous to Fermaid K, 1tsp/gal may be supplying approx 90 YAN, if my math is correct.
a. Best yeast for meads like coffee, blackberry and straight up?
b. Based on yeast selection, are there any nutrient needs that must be satisfied along the way?
I’m watching/reading a bunch online and very few include adding nutrients. But, I’m a fan of keeping my yeasts happy and decreasing their stress.
Regarding yeast selection and nutrition, this is your friend: https://scottlab.com/content/files/Documents/Handbooks/WinemakingHandbook2020.pdf
There are tables there that will tell you the nutrient requirements of each yeast and detailed descriptions of their flavor profiles. There is a spreadsheet linked in TBE's paper I linked above that you can use to calculate your nutritional needs.
Assuming fermax is roughly analogous to Fermaid K, 1tsp/gal may be supplying approx 90 YAN, if my math is correct.