10 Guage is only rated for 30 amps. You will need 6 guage. Look for 6/3 which will include 2 hots, a neutral, and an uninsulated ground wire (which is not counted as it does not carry current)
Here is your link to a 50' roll. However they will cut to length in the store...
You can swap out that breaker with a quad breaker. In essence it has 2 pole joined together in the center and another two pole joined together via bracket for the outside handles. Similar to this picture. You would still be limited to 20 amp due to wire size which is larger enough for the 3500W...
That looks like a single regulator with Dual gauges and dual outputs. The gauge on the left reads bottle capacity while the one on top reads your selected pressure to both outputs. Are you confusing the two gauges?
I take a plastic garbage can that is big enough for the Corny and the CO2 tank. Fill with ice and bungy cord a thick insulating pad around it all. Corny has stayed cold for up to 7 days.
I circulate boiling water from my HLT through the chiller and back to HLT for 20 mins or so. I then hook up to the BK drain remaining water to a bucket until I get wort. Then let it flow to fermenter.