The issue you have when using store bought juice is that you will be left with very little "apple" flavour.
However, a true hard apple cider like an English style cider should not be back sweetened. Traditional sweet or semi sweet cider is sweetened with Lactose.
I would avoid back sweetening with juice or fermentable sugar unless you have stabilised it first. While the yeast may go semi dormant at low temps, they will still be active enough to slowly ferment, even in a keg at low temps. This will give it a perpetual yeasty note.
If you don't like dry cider, then try lactose or try stabilising as mentioned above using sorbate and kmeta.
Sorbate coats the yeast inhibiting their ability to reproduce. This means you need to stabilise it off the lees. So you need to transfer into keg and then stabilise. The kmeta will scrub o2 and inhibit the yeast further. Combined, they will virtually eliminate the ability for the yeast to ferment. But they don't kill yeast.
Too much sorbate and you can taste it, so use it according to the right dosage. For kmeta, you really should know the free so2 in solution, but as a rule of thumb I would use something like 0.35g for 20L so you need a very accurate scale. Or you could do 1/2 a campden tablet. The kmeta will also help with shelf-life and oxidation so its ok.
Potassium sorbate should be added according to ABV, but at a standard cider AbV around 6% I would be adding 3.5g for 20L. It will break down in the presence of alcohol and produce Ethyl Sorbate which gives off celery notes, so if you over do it next time back it off a touch.
If all this is too complicated, produce a dry cider and have some apple juice to sweeten in the glass for those that like it sweeter. The downside to sweetening in the glass is you end up with a fizzy, apple juice like drink that isn't really cider like.
In my opinion, a good Bulmers type cider, served over ice and quite tart and dry is hard to beat. For that, I do the following
Preservative free apple juice from Coles or Woolies or Aldi. Make sure preservative free.
Dextrose to boost ABV to what ever you wish.
For a 5 Gal batch, a cup of tea with 3 tea bags in it. Let it go very strong and dark. This will give tannins which add that mouth puckering tartness and a little complexity.
For acidity, Malic acid is the acid found in green apples, and gives that apple tartness. Really you should add malic acid depending on the Total Tritable Acid (TTA) using an acid testing kit but a good rule of thumb I have found is about 3 teaspoons for a 5 gallon batch. If it's too much, next time scale it back.
I highly recommend using yeast nutrients, and use a yeast beast like EC-1118 which will tear through the fermentation.
All the cider yeast etc is, in my opinion a scam as Apple juice is highly fermentable and I have not found any difference using EC-1118 vs a cider yeast.
It's pretty cheap to make. Juice is around $1L if on special, some sugar and a few bits n bobs can get a 5g batch for around $30.
