wow. that is a lot of questions lol.

humidity is measured by a guage you can get at most pet stores. i leave all my bp's in there cages when i feed but i have 50. sometimes the stress of moving them into a smaller container can stress them out to the point where they will not eat.

and your thawing methods sound good. expect i submers the rat/mouse in almost scalding hot water. that way by the time i take it to the snake it is still hot not too hot but relly warm. your cage might be a tad to big but i would need to see a pic of the snake in it before i made that assumption. how long is the snake now???

and the yawing thing is proabbly not a big deal. he may be about to shed. are his eyes black or a whiteish tint to them?