well before i got my baby i was concerned about feeding exclusivekly on cgd.
I got my lil 6 month old male and i dont much like crix myself so i feed only cgd(until the other day)...i have to say all ive read suggests feeding only repashy CGD or sandfire but not komodo CGD ive read its not as appetisiing....
not that i eat CGD too!
THAT SAID....i fed mine crickets for a treat only a couple of days ago....and he caught them and swallowed them almost before they hid the floor of the viv! so i gueess you could say he was a little bored, despite my best efforts at putting loads of plants and climby things in there with him
a 30x30x45 exo would be fine i should think, and if your concerned about stressing the baby out in a large viv then you could always put a smaller 'faunarium' into the exo and pack loads of leaves into the viv to help the gecko to feel hidden.+
The floppy tail thing im not sure about...not heard anything like that...i certainly hope it isnt true as mine has stopped sleeping any of his 7 hides the last few days
now he sleeps behind leafcover on the side of the viv, and usually upside down!
Hope this sheds a little light on your questions and i dont think you have any reason to NOT get a crestie....size isnt everything and i think most could be weaned onto a CGD only diet with time and patience.