Apple snails need at least 2.5 gallons each. Mine have always done fine without heaters. They do tend to poop a lot, though.
IMO, apple snails are easy to breed. They have separate genders, reproduce sexually, and lay eggs above the water. They won't take over a tank like physids (pond snails) or ramshorns. They come in so many cool colors!
I've got a few golden babies left, if you want them! =)
Solstice - cellophane HM female