SPI, corner bead is easy. I do them last, too. I use vinyl bead adhered with 3M corner bead spray adhesive and no nails or screws. Metal bead with small galvanized nails is good too. All you do is stick it on per can instructions and mud it running your mud knife along the bead. The mud naturally feathers out onto the drywall. One coat is usually all that is needed. Just lightly sand if at all and that is it. On inside corners with the bead like on a window frame, miter the bead where the pieces meet on the wall. I did a similar install on a recessed light box but not sure where pix are sorry. I won't be getting to my window for a bit due to the holidays. I'll post them up when I do it but maybe you'll be into yours already. Corner bead is waaaay easier than inside corners so if you can do ICs, you can easily handle the bead.