I would like to make wine from juice I can buy in the store. I
understand I would need brands that are 100% grape, orange, apple, etc
juice. I think I also understand that I would need to add sugar to adjust
the sg. to about 1.090 for a medium table wine. Is that correct?

Of all the juices I see (frozen or fresh), most contain ascorbic acid or
vitamin C. I do not wish to use juices containing calcium or other
additives.

My main concern is is the ascorbic acid "OK" in the juice and/or do I
need to make adjustments in the amounts of acid blend (if needed) or would
I have to compensate by using just one or two types of acid such as
tartaric or citric acid to get the proper balance.