I am too cheap to pay for bowl blanks, so I make my own. My preference for marking out circles is to use a compass and/or dividers, scribe a line, and then round it off on the bandsaw. With log blanks, I slab it up first and then scribe the circles and then cut the rounds. If I get 2 bowls the same size, it is by accident, not design since I try to be efficient with my wood use. I don't do many natural edge bowls, but if I did, then I would use circle templates. If you do use a chainsaw, you need a pretty flat surface to cut the rounds or your bandsaw blade can get stuck and/or broken. I have a bunch of You Tube videos mostly about bowl turning. One is mounting things on the lathe. I do have another on prepping bowl blanks.
robo hippy