I only used three screws to attach this to the wall, and I filled in the holes when I removed it.
I use the high heat tape throughout the oven. I'm confused by your question about the glue. I don't use glue. I only use the tape. If you are asking about the tape adhesive, I have never seen any melting or any off gassing type smell associated with the tape. It is made for very high heat areas. If you are concerned, I would ask your local HVAC representative or plumber.
Mine wasn't super heavy, but molly bolts work best if hanging from just drywall. This particular wall is all studs, so I didn't have a problem hanging it. If i was worried about wall holes, I would use a hanger system like they use for cabinetry . . . a backer board if you will. Good Luck and hope your little enjoys your board.
Yes of course you can bake on it. Charcoal briquettes are the fuel you should use. The briquettes go in the pie pans at the bottom under the grill area. I have cooked pizza, brownies, cookies, monkey bread, and turnovers in this oven.
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I built one of these and also made an instructables. You are amazing and your son is super lucky. Don't let anyone tell you it isn't the best thing ever. My son learned caution and fine motor skills his peers haven't grasped. He problem solves better as well. This didn't help his already houdini like skills and I used, as I'm sure you did, parts that didnt match those in my home.
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