Hi Saw Dust
People that do it day in and day out just chuck up a Carb. Spiral Bit and cut it out but I would suggest using a template and a brass guide the top is not cheap and you don't get a 2nd chance at this one, once you have cut it out that's it so it must be right the 1st. time.
The template is cheap insurance and most sinks come with one.

or to say a full size patten.
Good Luck
Measure twice, cut once
Bj
