It sounds like you are doing good so far! I'm a new snake owner too! I'm not sure how thick the snake should be or why it looks thinner now, but as long as his/her spine isn't showing it's of decent weight. Also, you can tell if it's dehydrated if it has winkles in this skin. For example when it's turning you will see winkles in the bends of the snakes body. If you have water in the tank you shouldn't have to worry about dehydration.

A lot of BP owners say to feed your snake every 5-7 days, so if he/she will eat, I say go for it!

As for the shedding, it probably just had a bad shed. Keep misting and yes 60% is a great humidity. If it gets too high for too long you'll end up with scale rot.