I have made several batches of cider. If you want it sweeter, I'd suggest using splenda or truvia prior to bottling as opposed to more sugar. You can add some corn sugar to make it carbonated prior to bottling if you want that. Personally, I like mine fairly dry, so I don't add much if any sweetener any more (other than the corn sugar for fizziness). I've only used pressed cider from a local orchard, so I don't know how apple juice comes out, but I second the suggestion to use something other than champagne yeast. If you have a local brewery store, they can give you lots of suggestions. If it doesn't taste appley enough, you can add apple extract, although I've never done this.