I think EdWort's wife (German lady) drinks it with Sprite. He doesn't sweeten it, but does carbonate it.
I had some of Ed's 14 month old apfelwein a couple of years ago when he poured me a glass. It was SMOOTH! You should have a very smooth cider on your hands.
If you have to sweeten it (I don't like sweet things so I rarely sweeten any wines or ciders), you have a couple of choices.
You can rack the cider onto a solution of 1 campden tablet (crushed) and 1/2 teaspoon sorbate per gallon. Wait a day or two, to ensure it's distributed well and had time to work, then sweeten to taste with sugar, apple juice, honey, etc. It's easiest to pull out some of the apfelwein and add a simple sugar syrup to it. Take several samples and add different amounts and see what you like best. Take the SG of the sample you like the best, and then sweeten the whole batch to that SG. You'll have to do some math, but that's my favorite way to do it.
You can't carbonate the cider naturally if you use sorbate, though.
If you want to carbonate, you will have to add some fresh yeast at bottling, as I assume the yeast are long gone and the cider is very clear.
If you want to bottle carbonate it, you don't add the sorbate and campden, and you will have to add non-fermentable sweetener like lactose or splenda. Then prime and bottle.
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