I am new to the forum but have been fermenting cider for years. I have never had to add commercial yeast to get prompt fermentation started at room temperature. I bottle and refrigerate my cider after no more than 2 days at room temperature, or as soon as it shows signs of fermentation (froth, increased sediment, or firming/bulging of the plastic jug); if longer, the flavor suffers. I let it finish for at least 2 weeks in the fridge. I add no sugars or anything else. My cider is wonderfully sweet and fizzy (I live in upstate New York), and friends say no regional commercial ciders even come close. However, because I ferment in a closed container, usually with no secondary fermentation step, the alcohol content in my cider is probably pretty low (the sugar --> alcohol reaction never gets very far--the CO2 pressure stops it).
I got in the habit of slipping a tiny slice of unwashed, organic apple fresh from the orchard in each batch, knowing the apples had wild yeast on them.
UV pasteurization commonly does not kill all the wild yeast in the apple juice, however, and I also found that my fresh-pressed, UV-pasteurized (required in NY state if no preservatives) apple juice still turned into delicious cider even if it beat me to it and started bulging out of the plastic bottle before I got around to adding anything to it, bottling it, or refrigerating it.
• As above, buy no apple juice/cider with sulfites or other preservatives.
• You can start your cider 3 ways: depend on retained wild yeast in the juice as sold, add a bit of organic apple (the less sprayed in the orchard, the better), or use a commercial yeast (tons of these--see these forums), sold for beer-making, for wine or champagne, or specifically for apple cider.
• There are a bazillion ways to make cider on here and get the flavor/fizziness/density/ABV/sweetness you want. Just look around!