The correct pressure is a result of your desired carbonation level's, in volumes of CO2. This is dependent on the temperature of the beer. Let's say you want 2.5 vols. of CO2 in your beer, and it was at 39-40F, you would need about 12psi of CO2 applied head-pressure the entire time, until keg is consumed to maintain the 2.5 vols. of carbonation. As far as your line's go, you need to balance them to the example above, not turning the CO2 pressure up & down to maintain carbonation level, as so many do. This is a result of a un-balanced system, either too much or too little resistance, but usually too little. If I were you, I would use 8-10 ft. 3/16" vinyl line and use the set and forget carbing method at 10-15psi for most beers @ 38-42F to achieve and maintain the right carbonation level. If your impaitent, you could use the quick force carb 30 psi method for a day or two, but it can be very inconsistent, and result in over-carbed beer that's hard to get back to equillibrium with the 10-15 psi needed, thats built into the system. Once it's over-carbed, we start playing the up & down,vent the pressure game, trying to get it too pour right, without foaming allover, thats the excess dissolved CO2 coming out of solution, and coming to equillibrium with the only,10-15 psi of head pressure now being applied. This is why I prefer the set-and-forget method better, albeit, it takes 1-2 weeks to get a good carbonation level, in my opinion though. Hope that help's!! Cheers!!!