Yes, that is a lot of cherries. The Concentrate I use has this in the product description "1 Serving of Tart Cherry Concentrate equals 2 cups of Fresh Cherries! " (1 Serving is one oz of the concentrate with 7 ozs of water) So figure from those numbers.
We just shared a bottle of Tart Cherry wine with some friends. The wine is full bodied, very tart with very little indication (Sweetness) that it's SG as bottled was 1.018 (Back-sweetened to that from .995) It was made from Montmorency Cherry concentrate.
That batch was 3 gallons made with 3 x 16 oz bottles of concentrate. Each bottle was supposed to make 1 gallon of Tart Cherry Juice. Additionally I used on 16 oz bottle of Dark Sweet Cherry Juice concentrate also supposed to make 1 gallon of juice. I'm not saying that you won't get a good wine with less than that but this is one solid wine and I have another batch aging right now that will be ready to bottle next May/June.
As to waiting for the cherries to free up the sugars, yes that's true with all fresh fruit. If you don't crush the fruit or run it through a juicer you won't get a true SG reading until the fruit as broken down enough to free the sugars. That's one reason many people like to freeze their fruit before crushing. It tends to break down the fruit pulp. BUT that's also what the Pectic Enzyme does too. That why it should be the first additive to your cherries or any fruit. Let it get started doing it's job ASAP.
Also, a lot depends on how ripe those cherries are. I have a tart cherry tree and I frequently start picking a bit early, only to discover that there are many shades of red and only the darkest red ones on my tree are truly ready. Hopefully in about 3 years my 4 new tart cherry trees will start producing to some extent and I can make cherry wine from home grown cherries.