Actually column tanks are pretty limiting due to their height and constricted swimming areas. I would't do the neons, they need more horizontal room. The corys would be cramped too. The DG is debatable, not sure whether it would work or not. The guppies would work but they are high bioload fish and will take up some room, plus they tend to breed easily. Nano fish might be a better option, such as ember tetra, chili rasbora or celestial pearl danio. A shoal of 8 of one of those with maybe a pair of scarlet badis and some shrimp and maybe a few endler's livebearers (similar to guppies but smaller) would be a nice tank.
