To answer the question about fermentation and maintaining CO2, there are two ways to do it. You don't have to stop the fermentation process short to maintain fizz, as Tony said. If you get it right to the point before the yeast becomes inactive, when you go to the bottling process, all you do is add a small amount of sugar (one that is specifically used for carbonation, called priming sugar) to the bottle, and cap it, which will create a sort of secondary fermentation, giving you the carbonation. Or, you can force carbonate, as you mentioned, Josh, with a CO2 source pressurizing the keg for a set amount of time (more pressure, quicker carbonation process) until you get fizziness back that you want. It's easier to control the level of carbonation with this method, because you can change the pressure and duration, instead of just changing the amount of priming sugar used. The way that Tony described could work, but is not at all necessary.