Inside First Room

Having excavated as much as we wanted in the first room (the furthest West) there are a few questions which we can't answer.....

1. Why is the North wall stepped out at the bottom yet the West wall isn't?
2. Why is there a big gap in the middle of the floor?
3. On the North wall there's 1 stone that protrudes and on the top face has been chiselled out so there is a recess - why?
4. Lots of coal dust on the floor - what was it used for?
5. The East side of the room has a nice stone flagged floor but the other side of the "gap" it's rough, why?
6. Are there signs of burning on the West wall half way up?