Hanging the tanks on the wall will not get you much in the way of usable floor space or look very good either. Why not something like a free standing wardrobe closet with the tanks on the bottom and everything else above them? Something that looks like a piece of furniture as this will be sitting in your dinning room. Four sets of doubles placed 2x2 should not be too deep or too wide provided there are no backpacks or BCDs left on them.
It's not so much the floor space as the bending over and picking them. Much easier to lean back and slip into them. They don't stay "stored" very long so it's not just a matter of out of sight out of mind.