What was your s.g. when you started? If you ferment it fully dry (.990), you'll have the potential alcohol you estimated, but you might choose to drink it at 1.000 or 1.010 and that would of course change the ABV. You could ferment it dry and backsweeten it, too. It's simple to take the s.g. before pitching the yeast to get the potential alcohol and take the s.g. when you're finished.
For wine, you should use regular granulated sugar. You don't get a cidery taste in wine with regular sugar, because you don't use malt extract or grains like you do for beer. Regular sugar is the best for wine.
Here's my grape juice recipe (from the winemaking forum):
2 cans (11.5 oz) Welch's 100% frozen grape concentrate
1-1/4 lbs granulated sugar
2 tsp acid blend
1 tsp pectic enzyme
1 tsp yeast nutrient
water to make 1 gallon
wine yeast
Bring 1 quart water to boil and dissolve the sugar in the water. Remove from heat and add frozen concentrate. Add additional water to make one gallon and pour into secondary. Add remaining ingredients except yeast. Cover with napkin fastened with rubber band and set aside 12 hours. Add activated wine yeast and recover with napkin. When active fermentation slows down (about 5 days), fit airlock. When clear, rack, top up and refit airlock. After additional 30 days, stabilize, sweeten if desired and rack into bottles.
You don't absolutely need acid blend and pectic enzyme or yeast nutrient, but it makes a difference between "drinkable" and "good". Wine yeast is necessary. If you have a LHBS, you can get those items for a couple of dollars.
You definitely don't need special grape juice concentrates- you just need to make sure the juice you use is 100% juice. The purple (red) is made out of Concord grapes, and the white is 100% Niagara grapes. Don't get the juice with high fructose corn syrup or added sugar. Welch's is really the best for this.
Don't use an airlock until fermentation slows down- just cover it loosely to keep bugs out. Wine ferments less explosively then beer- it'll go slow and steady without a krausen.
Now, that's the last of my advice. I can't be of any more help to you except to tell you to read up on this stuff yourself.
Lorena