I have the 2.5 Metalcloak with dual rate springs and Rockport long travel shocks. It rides better than stock with no swaying. I haven't had a Teraflex kit, but wouldn't be surprised if they are fantastic, too.
I just did this. I was trying to keep my stock wheels. After researching wheels/tires/lift, I went with a Metalcloak 2.5" lift. In order to keep the stock wheels, I was going to have to either get 2" spacers or buy new wheels. In the end, I opted for new wheels. It's really a personal choice...
To be honest, I have no idea. Power Tank has a table that gives approximated usage.
I got the 10 lb. tank and have 315/70/17 tires. I'll be using a Morrflate system to air all four tires at once.
Power Tank is sending pre-Black Friday codes out to VIP subscribers. I ordered a JL kit. I also made a mistake and forgot to add an upgraded aluminum knob. I contacted Power Tank and they made it work to ship in one package. Great customer service!