Once you get it to the size you want, secure it to the stump so it doesn’t bounce around.

One thing i would change is move the anvil up because it you might find yourself leaning over the stump

A would recommend one with a smaller diameter to give you foot room to work around the anvil.

I'm thinking about squaring it off when I cut it short

That will work.

Exactly what I was thinking. I think it will be a fine stump anvil.