30X30X45 is no way big enough for 2 adults, certainly not 'comfortably' anyway! except maybe when they're asleep!!! i have about that size as a temporary separation tank for a single adult.
Babies are tiny you're right, so if you get a hatchling then house it in something not too big, but height is always good
Adults do great in the 45X45X60 tall exo terras. They love it.
As for the cresties, theyre fantastic! im hoping to breed in the new year so if you decide to get the brb 1st maybe ill have some good looking babies around the right time!!