re: Anyone cooked meat directly on charcoal before?

Make sure you use natural chunk charcoal, not processed charcoal briquettes that have fillers in them.

And no, you're not crazy. One big thing is to get a hair dryer or a fan or something and blow as much of the soot off as you can. That's what will give it an ashy taste. Don't leave the meat on the fuel for very long and you should end up with a nice fajita.