The rack dimensions will depend on the size and shape of the tubs. They should fit well but not too tight.

The enclosure I'd look at plexy glass or lexan instead of glass if you are hinging it. it is way easier to drill. If you want glass I'd buy it at a glass place it is usually cheaper and often they will have glass track so you can have sliding doors that is easiest with glass.

I'd HIGHLY recommend PVC for the floor it is easy to heat though and clean. The heating a wooden enclosure is hard at best. The pvc floor can be screwed and fastened just like wood but it is hard to glue so think mechanical fastening. (NOT PVCx it is also harder to heat through. Better insulator for tops however.)