apple snails, aka mystery snails, are poop machines if fed properly. ample filtration on a tank with apple snails is a must, as is regular gravel vacs and water changes. a ten gallon would be able to house two snails with your current fish, IMO. and if you do end up getting egg clutches, just freeze them in a ziploc and toss them in the garbage. call it brigg birth control, lol.
i keep and breed briggs (Bridgesi), and they are messy when cared for properly. they need to be fed at least every second day, and will scavenge the substrate, decor, plants, etc for leftovers in between feedings. they do not eat plants but may cause damage to the more fragile plants in their travels about the aquarium. a higher ph is necessary to keep shells in good condition (mine is 7.8). yes, they need both genders to propregate. they will float about in the tank for a day or two sometimes, just to worry their human needlessly, lol.
as for feeding, all fish foods are good for them, but snail jello is the best, as the extra calcium is necessary for shell quality. there is a sticky in the invert section here on AC that has recipes. various veggies are good too, zucchini, french cut green beans, cucumber, lettuce (but not iceberg lettuce for some reason), are excellent. my snails go nuts for bloodworms, and i believe the bloodworms are what changed the pigmentation of my ivory's shell to magenta.
