Sugar amount should be determined by you SG with a hydrometer. Sugar content of berries depends on how ripe they were when picked, so you need to check with a hydrometer. Normally I just make up a batch of simple syrup (2 cups sugar to 1 cup water) and start by adding that for 1 gallon of wine. That will get you in the ballpark. Also check the acidity before you get ready to pitch your yeast.
As to growing blueberries - It's all about soil prep. Pine needles, sulfur chips and fertilizer for acid loving plants are my main tools. Soil here in NW Arkansas is also akaline but those tools help overcome the problem. Also mulch with pine needles - Makes for a nice smelling berry patch too. Do soil prep well before you plant and treat a large area dig your planting hole 2-3 times the normal size and treat the daylights of it. A full cup of sulfur chips and several large handfulls of pine needles mixed into the soil. After planting I treat my beds with sulfur chips about once a year and fertilze fall and spring (Before they bud out) I've lost some plants too but found that if I go BIG in buying plants, they do better. Get the largest plants you can find - If it comes a container less than a gallon - don't waste your money. They also will be producing much sooner that way - generally buy the 3rd year you can be getting several pounds of berries off a plant.