I can not comment on the CO2 stuff because that is not my expertise (I only have a 10G tank), good luck with whatever you choose. As far as the design I think you should move the driftwood to the left and also reduce the number of those large rocks. Right now when I look at your last picture, the order in which I see things: 1) centered driftwood/fern 2) large rocks 3) Buddha 4) everything else. I remember reading that one of Amano's principals with rocks is always conceal your intentions, don't let them stick out too much. And also, I hate to say it, I love the Buddha, but we all reach a point when we have to remove such things from our tanks because they ultimately distract from the natural look of the tank (I know because I had to remove one of my sunken ships from my tank!
) I guess its a matter of personel taste, so really its up to you, good luck
