I Think the price is ok. Not great but not high either for 6 gallons. I pay about $10.00 per gallon for my concentrate so that's a little higher than yours but your fresh fruit is not cheap either so, it sounds reasonable.
Interesting that they don't tell what variety of cherrys the sour cherry concentrate is made from. They may just source it from the cheapest supplier of juice/cherries. Some companies specify exactly what type fruit goes into their juice. Does it matter? If your really want to know what's going in your wine then yes. With grapes there is much to do made about the grape variety and even the vineyard it comes from. (Northern California vineyards are better than central California ones- Really??)
1) Remember to add volume to your starting point for the loss of gross lees from the cherry pulp. Even in a pure concentrate with no pulp you will lose a significant amount to yeast and other material that will form and precipitate out. For my recent blueberry batch I started with just over 3.6 gallons and barely had 3 gallons when the pulp came out at first racking and that was with 16 3/4 pounds of blueberries. Cherries and blueberries should be about equal in the extent to which the pulp breaks down into liquid.
2) Some will say you cannot have too much flavor but.... for most fruits I believe there is a tipping point where you are wasting fruit/money adding more and more for very little return
3) Mixing tart and sweet cherries is a reasonable thing to do but I think most allow the tart to be the dominant one. It's really more of a personal thing to be honest.
The additions -
Acid blend only to get to the pH start point you want. Most fruit wines do best somewhere between 3.4 and 3.6 as a start point. Do NOT go higher (3.7 3.8 etc)
Tannin - Your choice - check around about recipes for cherry wine. With a dominant tart cherry you won't need as much if you do use it.
Yeast - Your choice. Some of us don't refine the yeast choice as much as we could for the wine type. Some have a favorite yeast and stick with it as an old faithful part of their wines. Others try to fit the yeast to the exact wine type. Whatever you choose make sure the needs and characteristics of the yeast are a match for your wine making environment. ( Temperature, pH, yeast nutrient needs, type of wine and of course ABV.)
