The only time you run into issues with Ethanol is if you have been running straight gas for a while and then switch. The ethanol dissolves the built up gunk.
If you run it from day 1 it never builds up.
If you are getting phase separation due to water getting in the gas, fix the leak that's letting rain water in (or put it in the garage). I ran the numbers one time for a worst case scenario on a 200gal boat fuel tank. Over the course of the winter, worst case from the airborne moisture, it was about a teaspoon of water than could be squeezed out. In a 1/2gal lawnmower tank it wouldn't even be a drop.
A little fuel stabilizer isn't a bad idea but not really critical.