You're going to get different answers from almost everyone it seems.
1: You may want to wear a base layer under your jersey/shirt it can soak up a bunch of the sweat
2: I find that as long as its not European most 2X bike shorts should fit, the Sugoi and Loius Garneau 2x Bike shorts fit myself.
3: I use a bike computer mostly to watch my heart rate and check to see if my mind is wandering and my cadence is falling off.
4: Co2. It can get hard pumping the tire up over 100psi without a special kind of frame pump. And the CO2 is so quick and easy and small.
5: You'll get use to it as you go on, I was about one 24oz every 20 minutes when I started, now I'm about 1 an hour.
6: I think everyone is planning their next bike purchase as soon as they get their new one. Bike shorts can help with the comfort.