I use 12 qt tubs on my neos. I would wait until about a year before considering a viv. There is actually a lil viv set up on MVF (will post link at bottom). It's a small set up, but you can elaborate however you would like. After the first year or so I would see no problem putting a chondro in a smaller adult enclosure. To me 24 cubes are ideal and I would not change it. If you plan on using 36x24x24 I would use a smaller cage until around 3. Also, if you get a baby, I suggest a basic tub with UTH and a reostat. I've used this set up on several neos and never ran into a problem. Also, as a new chondro keeper I suggest getting a yearling. It sounds like it will fit into your plans better, and it's more hardy.