As far as the sugar you would use that a matter if opinion. Cane sugar is used a lot becaused once it ferments out it has a neutral flavor (plus it's cheap). I'm not sure what kind of flavor dextrose will give you.
The best way to to get a sweeter wine is to let it ferment out to 1.000 or lower, stabalize with campden and potassium metabilsufite, and backsweeten a little at a time time you get the taste you want.
I would say that you will definately want to pectic enzyme 24 hours before you pitch. Same with campden (especially if you have doubts on the fruit). As far as acid, engergizer, and nutrient that is totally up to you. If you use some of your blueberries in the primary you'll get plenty of what the yeasties need.
Hope this gives you a starting point.