I think you'll only need one packet of yeast, each packet is good for up to 5 or 6 gallons. As far as the PS and Campden, if it's pastuerized apple juice from a store then you shouldn't have any problems. Really I only use those for my ciders that are made with fresh pressed cider.
As far as a (rough) time frame, give it about a month in primary (until fermentation slows), then a month or so in secondary (until clear enough to read a newspaper through), then (optional) rack again into bulk aging for 3-6 months for Malo-lactic fermentation to take place. As long as it's cleared and the SG has stopped dropping, you should be safe to bottle, but if you can wait, it only gets better with age.
"Give me yesterday's bread, this day's flesh, and last year's cyder." - Benjamin Franklin