Welcome to AA, soccerjohn!!
Should I leave the airstone going to keep O2 in the tank or unplug it?
Leave it. Is there a filter in this tank? If not, an easy filter that I use in smaller tanks is to use a AC
sponge, cut an X in it and thread the airstone through.
There is a snail in there also. Is that ok?
Use finely crushed flake, or Fry Bites, or baby brine shrimp as food.