Definitely late to this party, but I'll comment anyway.
The black rings sometimes supplied with Asian import buttons are not at all intended for installation above a panel. I've seen them used this way and it looks ridiculous. The only reason they exist is so they can be mounted to thin metal control panels, while using the shoulder to set them into place. I.e. the rings are nothing more than spacers which allow the nut to clamp them onto the underside of the metal panel. Without them, the nut cannot be tightened enough to make contact. Also, using them to adapt to a larger hole is usually a non-starter, as their OD is often too close to the OD of the bezel to offer a secure mount.
Virtually any size bit between the body diameter and the diameter of the bezel its can be used, so long as there is reasonable support under the bezel. Yes, the hole will be a little large in some cases, but the nut will tighten down and prevent the button from ever moving. There is no absolute need for precision with the button holes. Folks should also understand that wood and plastic shrink and swell depending on the humidity of the room. A tight button hole may eventually lead to operational issues. A little extra clearance is always a good idea to prevent this.
A spade bit doesn't make a clean hole like a Forstner bit, but the bezel will cover the edges, so no-one will ever know. You CAN use a Forstner bit in a hand drill, but it can be dangerous to your wrist, as they have a tendency to bind in the hole if not drilling perfectly straight. If you absolutely must use a hand drill with this kind of bit, make absolutely sure that you use a drill with a clutch and adjust it just tightly enough for the drill to do it's job. Hopefully, this way if the bit binds, the clutch will break loose before your wrist does. I don't recommend using them this way at all, but I have done it a few times when I was too lazy to set up the drill press.
CNC machines allow for any size, but they also allow one to try to be too exact, leading to tight fitting buttons (not a good thing.) But once you get one, learn the machine and factor in the correct clearances, you'll never want (or need) to drill a button hole again