Most tapers place the metal corner bead first. This is primarily because if you were to do any taping first you'd have to wait until that dries to install corner bead. It's a matter of efficiency.
It's also usually best to keep metal bead set snugly to the drywall, with nothing behind it. This allows you to keep it straighter and on plane. It should protrude just slightly on both walls when a straightedge is set against the drywall perpendicular to the bead. "Tucking" the tape under the bead does nothing of value. There's tape all over the building that's not tucked under anything and it's not an issue.
All that said, drywall taping is something of an art and you're free to do what makes sense for you and your project. Just remember the cardinal rule: lighter is better. The pros I've worked with do very little sanding to produce fantastic results, and it's far easier (and less messy) to skim on another coat than to grind down humps.