I have been reading here that young snakes feel more secure in a smaller enclosure. I have also read that many people keep their snakes in click-clacks for a year or more. I don't want to do that, I want to be able to see what's going on (watching a snake cruise his enclosure is very relaxing!

) However I don't want to stress out our new snake. Our first snake was just bunged straight in his large enclosure and never seemed to worry, but he was a bit older. So my questions are:
1) When is an appropriate age/size to put a snake in a larger enclosure - the enclosure is ready so it's not a case of keeping him in a click-clack due to lack of space or $.
2) If I move him and he stresses, moving him back should decrease the stress?????Yes????
3) How do you tell if a snake is stressed?
4) For a small snake (4 months old) how big is too big for an enclosure?
All and any advice would be appreciated.