Pinky anything is too small for him. He is likely under fed and therefore looking skinny.

I feed a rodent 10-15% of the body weight every 4 days for a guy his age.

The stringy stuff could just be urates and poop. Sometimes BP poop looks weird and most of the time it is nothing. I would clean it off and see how it looks.

As far as hiding goes, that is what they do. A happy BP hides all day and comes out to look around in the evening. But a lethargic under fed one can do the same.

I suggest double checking husbandry, then getting a scale and sorting out the feeding, and the rest will likely take care of itself.