I've made a couple of batches of concord with Welch's. They've turned out to be a great tasting wine. I take Jack Kellar's recipe from his site and multiply everything by 6, for six gallons. I don't follow the sugar measurements, I just add sugar until I get the desired hydrometer reading, which I like this wine for my family's taste budsand my friend's taste buds, which is around 14% to 15%. I then add potassium sorbate, wait a few days, then add sugar back to get desired sweetness. Ican get a better recipe together of how I make it so that itmight be a little easier for you, but like Waldo said, there is no substitution for the knowledge that you'll get from this forum as well as Jack Kellar's excellent site. By the way, Jack mentionsto use 2 cans of the concentrate, but he states that you can use 3 cans instead of 2 cans for a more bodied wine. I like using 3 cans per gallon, for a six gallon batch I normally use 17 cans total. This is going to mean that you need to adjust the sugar because adding more concentrate is actually adding more sugar also.
I've tried the Welch's white grape/peach and the concorde, as well as the 100% apple concentrate from an off brand and all of these wines turned out to have a very pleasant taste to the pallet, LOL. I like the kick of the wine, but the sugar added at the end, before bottling,makes for a very nice sweet wine with a kick!
Please post any useful info you may run across as I'm still a beginner also, I really enjoy reading winemaker's stories!
Muscadine