I ended up taking out the vent and filling it in. Venting out the front is fine. Ideally yes, I would build the archway longer and stick the vent pipe in the arch. This would also help with wind.
24" is too small. Go 30" at least. 30" I think would be fine to have a good amount of very hot coals and easily fit a small 12" pizza in for 90 second pizzas. You'll never do more than 1 pizza at a time though. But properly insulated, with a small fire around the sides and cook lots of pizza I bet.
My problem is that I left this out in the rain for 9 months, and it ruined my FB Board insulation (underneath the floor). So the top, even with no insulation gets hot and stays pretty hot (it's not losing any heat to conduction) where-as the floor will just not stay hotter than 700F. You can feel the bottom of the 5" concrete slab getting warm below the FB Board.
This was my first pizza on there, that was like 60 seconds I think it could have gone another 30.