I wouldnt worry about not seeing his poop yet, as already mentioned, it can be hard to spot in substrate when the snake is young. You'll soon start to notice it as you find out what to look for, I know with mine I couldnt find any for ages, then started noticing the places he likes to relieve himself! Mainly around the edges of the tank or around the edges of the cork bark log I have in there.
Already as mentioned above, I would step up his feeding to around every 5 days, if you check out the munson plan on this forum, it will offer lots of help and comes highly recommended.
Finally, regarding it hiding, that is what they do most of the time! They rarely explore their tank much in the daytime, im sure you will see more activity as it gets a bit older, a bit more confident, and certainly in the evenings and at night time. Arlo my ghost normally comes out every evening and sits in his plants on the side of the tank, although he doesnt explore too freely when the lights are on in the room, last week I came in quite late and it was very dark, I flicked the light on and he was spread across the tank and his head was pushed up against the front of the glass!!
Good luck though, and if you havent already, post us some pics!!