Is there a minimal tank/cage size requirement for reptile?

Young snakes can get nervous in very large spaces. I think it is a combination of the fact that humans appear as predators, and the larger space is daunting. All snakes should have hides, and if you do put a neonate in a largish enclosure, they should have multiple hides. It helps them to feel secure. I learned long ago, that in the long run, the more places you have for a snake to hide, the more likely you are to see it out and about. If you have a tame established adult animal, that you have owned for a while, and is used to you, you can really give it as big of a cage as you want. Any time you move a reptile to a new enclosure, it can be a bit stressful. So it will take at least some time to acclimate to the new cage.

That is my general rule for minimum cage size of a sub-adult/adult. Height again depends on the species. A boa constrictor or ball python won't utilize the height as much, so i wouldn't consider it in factoring if the cage is big enough, just L x W. They will use it some, especially if you put ledges or shelving of some type in, but it's not a factor in "necessary space". An arboreal species though, you can consider height as a factor. a 6'-7' emerald tree boa could be happy in a 3'L x 2'W x 3'H cage, as long as you have branches and perches at different levels. They will go up and down as much as they side to side. I would say that same cage would be too small for a 6'-'7 boa constrictor though. As a general rule for height for heavier bodied terrestrial species, 1' is actually fine. I prefer more, I think it is nicer looking if you are going to spend the money on caging to spend the extra $40-$50 and get the extra foot of height, and use some type of platforms or rocks the snakes can utilize.