1. I use a pure O2 system as well. I don't 'swear' by it, but it sure is a nice item to have around. I've cheated by underpitching, oxygenating a bunch, and then after some lag while the yeasties grew to a good colony size, had great fermentation, proper attenuation and a good beer.
3. I think most recipes assume you'll add the right amount of priming sugar. While there are style guildlines for carbonation, in the end it matters what YOU like for a carbonation level in a given beer.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10