I am having the same issues (except for the pooping part) as you are and my cham is almost 6. He also has been healthy up until the last few months. I have assembled a net and also going back to his smaller cage. I was also told it was old age setting in as their life span is usually 5-7 years...
My guy did this too. I also agree you need to put the cage up higher. I have mine sitting on a old end table I got from CCA it cost me about $6.00. He also would climb on the cage when I came in the room. So I started opening the cage only to find he just wanted to visit.
sick cham
I would try longer mist times fewer times a day. My timer is set 3-4 mins twice a day and a good 5-6 once a day(I would do that in the mid day you don't want the cage all wet after his lights go out). I also agree with all the feedback you have received. Good luck! :)