Hey Flp, is there like a name I can call u then simply that?
Anyways, I'm new to water monitors but I can tell you what I learned from research and a bit from experience.
For your first question, yes some water monitors species grow smaller or larger than some other ones, especially with the V. salvator cumingi which is usually a lot smaller than the other species. However, most of them will grow about the same size and length as the others. Even large types of water monitors can be small because they each have their own growth speed and max length like us humans, etc.
The temperature should be the same with water monitors and monitors overall. Of course if it is desert it requires sandy environments and a more hot and dryer climate than the forest species. 75F at night, 85F day, basking spot around 100-110F. You can raise the temperature during summer time.
The average size of an asian water monitor is 6-7ft. This is not in my wording but dozens of professional monitor owners I know, dozens more from what I heard from petshop workers, and countless info from the research I do on the net. You should feel lucky if it reaches about 6ft. I'm aiming for a 5-6ft monitor because I dont care about his size, I love him even if he never really grew. I've been to the eastbay vivarium and they have a large monitor there name Spot which took 5 years to reach 7ft. If anyone don't believe me, they're in the phone book so call them. Babies cost about $150 but I bought mines cheap from a friend for $100. Remember to pick one with good coloring(not neccessary), good size, bright eyed, flickering tongue, and a good appetite with no molting problems, etc.
JamesDarec