1. follow the instructions that came with your powder, I dont know where you got it from, I dont use the powdered stuff since we have the liquid stuff, but powdered will work just fine.
2. Staggered Nutrient Addition, I recommend you go to the Scotts Lab website and find their winemaking guide, its free, it explains a lot of things like staggared nutrients. The basic idea is that if you feed the yeast to rich a diet high in nitrogen from the start they get fat and bloated and dont work as hard and dont have a tough membrane because they grew to fast instead of a nice steady nutrient supply. Dont fret about it too much, many people just dump it all in at the start. The sugar break is just when 1/3 of the sugar has been consumed. Things are different if you are doing a high gravity mead.
3. Do a Total Acidity test on your juice before you add any honey to calculate how much acid they have, berries will of course vary in their acid content, if you are using Euro dried elders they will be different than American Elderberries, so 93 is just what we had to add, your mix might be different, better to go ahead and learn how to do a total acid test now so you can use it for all your future wines.
I really like Pasteur Red for this, and the K1V1116, but many other yeasts would work.
WVMJ