I personally have a 7 high 41 qt set up (home made). I can fit 41,28,15 qt tubs in there fine. My logic is if you build of buy it, do it big because they can never out grow a 41 qt rack but you can always fit smaller tubs in it.
As for you I have a few 1 year olds and they are in a 28 qt and I actually have a 8 month in a 15 (she eats in it, was on a 3 month fast til I moved her down and she is eating like a champ).
Flexwatt is at ReptileBasics
Hides HomeDepot or Lowes use plastic flower pots and cut to size
Water bowls use ceramic water dishes.