I am in no way an expert when it comes to baby Greys but at 7 weeks I would have pellets and small chunks of veggies and such in there for him to nibble on. Most of it will only be played with and soiled but it is a good learning experience. My baby who is about 1/2 a week younger than yours already rolls a ball around her tank, so I would suggest you putting a couple things in there for him to play with such as a cockatiel ball, medium sized wooden bead, etc. Every 3 hours feeding seems a bit much to me. My girl is on 4 feeds a day. Some would say she should be on 5 feeds a day but she simply won't eat that often and seems to be doing well on 4. Try increasing the amount fed at each feed and spacing the feeds out a bit more. Depending on your Grey's feathering and the ambient temperature of the room your keeping him/her in, your grey should be ready to be moved into a cage in about a week.
Maybe someone more experienced in Greys will come along and give you better info. Like I said, I am no expert in baby Greys.