Now that the rosette is firmly glued in we can cut out the sound hole. I do it this way, starting on the drill press a hole is cut large enough to fit over the sanding tube.
Be careful to leave plenty of room between the bitt and the eventual edge. The drill can tear wood.
now you can carefully sand to the hole size that you desire. Go slowly, if you over sand you can't get it back.
This feels about right to me. What do you think? Most luthiers would probably do this with a router and a fancy jig. I confess to being a little old fashioned and prefer to do this by hand.