he isnt super fat at the moment. maybe as fat as a sharpie? When i first got him he was maybe a little fatter than a pen? these are mearly estimates though. I assume you are asking this because you want to get one and put him in a smaller tank before you upgrade? What size tank are you looking to put him in?
that is a good sized tank for him
many people say for snowflakes, that if it will fit in his mouth, he will eat it. But this depends entirely on the eel itself. They are invert eaters by nature, but some have been known to snack on a fish. Some will not even eat your shrimp, hermits, ect. The best way to make sure that he wont, is to expose him to them while he is younge. Then he will no longer think of everything there to be a food item. What fish do you have that you are worried about him eating?>
as long as the fish are large enough to not fit in his mouth he will not eat them. mine is about 15" and about as big around as a highlighter. i saw one yesterday at the lfs that was over 2' long and about as big around as a waterhose, so they wont get too big. about the only thing you might worry about is your inverts.