my corn snake...
is young and about a foot in length and very thin. he was in a 10 gallon tank until yesterday when i upgraded to a 20 long. i believe that he was having some difficulties in the small tank because it was more difficult for me to control the heat. there was really only warmth in there, no cool side. i had leaves and a hide out for him and drift wood, but he was very inactive and rarely came out to explore. i would turn the light out at night or forget to turn it on in the morning and i'd go and look and he was out and about, chillin' like a villain on penicillin. he seems to be doing much better already in his new tank, he was hanging out on his vine this morning when i woke up. i definitely recommend you start with the 20 gallon tank. i don't see how it would cause issues for the little serpent.
ps- i feed norbert inside his terrarium, i am just careful. he does strike if he's a) hungry, b) about to shed or c) if i sneeze on him by accident. jk about c). he thinks my hand is food, no doubt, but i don't really worry about it, i usually wrap cloth around my hand when i want to take him out, he sees it and knows it's not food, he just slithers away, he doesn't strike. i've been bitten, it doesn't hurt, it's actually quite thrilling in fact. when he gets bigger i will have to feed him elsewhere, but for now it's all good in da hood.