I cut several hundred 10" and under tress flush around 1991 and regret it to this day. I hit them often when brush cutting. They rose up a bit over the years, or the dirt around them eroded. Either way, they are up to where I bump into them. Any I've cut since, I've left tall enough to see them over the grasses and wildflowers that grow up now. I can go around them. Until I get something to puck them out, I can at least see them easily.
So take it for what it's worth, but cutting them flush is pretty hard without getting your chain and bar in the dirt. Until you get something to dig the stumps out with, leave them taller, and the taller the better for leverage.
Have you thought about just spending the money and renting an excavator with a thumb for a week and just getting it over with?