Wow. 40 somoalians for a 20 pounder? Sounds too good to be true. But if all is good, then go for it. It probably isn't going to be new. Make sure you have a place nearby that will refill. I've been reading from others that that is not a guranteed thing anymore as some companies want to rent you a tank and then they fill it. Sometimes, depending on locale, that may be the better option. On the size, the bigger, the less trips to refill, but I might add some caution. Since this is your first time, make damn SURE that all your fittings are tight. I mean, teflon take the threads, torque them down like a SOB and soap test and then test some more. I lost a full ten pounder from my impatience. Also in the 4912, you can run the CO2 line from right under the metal plate, there is a plug that comes out with some needle nose pliers. Right below that is a drip pan. That is a really tight angle and make sure your line doesn't get kinked or you won't be getting any right amounts of CO2. Mine is within 6 months old and I don't know how you can get more than 2 lines through that drain plug so if your going to use a manifold system, look at having that setup inside the kegerator. You'll have a lot more room if you take the door panel off from the inside.