That tank should last them for a while if you get pups, a year or two, not for life.
Any ray produces alot of waste.....
A ray costing $1000+ should not be treated as hardy even if they are... It would be a big mistake if one were to take their hardiness for granted. But yes, i hear leo's are hardy due to the fact that they are not dificult to get eating a varied diet... But still require great filtration and lots of water changes just like any other ray.