Well that depends on how "hard" you want your cider.
Many people enjoy 5-6 percent ciders, some want much harder, you can sweeten with honey (a particular favorite of mine) to add alcohol, brown sugar (goes well), molasses, table sugar or the saccharide of your choice.
Take an SG reading of it, and see where you are at. That will give you an idea of potential ABV. Then determine where you want to be. Notty doesn't attenuate very high so you will end up with a sweet product, but you may have to add sugar if you want something very stout.
Carbonation is up to the maker. Some make still, petillant, or sparkling spiders. I'm not really sure what volume level you go past to get to each. Still is obviously flat. Petillant I would imagine would be something around up to 2.75 or so? Sparkling higher.