They should be fine without a heater as long as you have them in a heated room in the house.
filter is just fine
My snails really like a slice of zucchini zapped in the microwave for about 30 seconds. They devour it in a day. As long as you provide them with food on a regular basis they will breed like rabbits. MTS are livebearers and will begin to produce quickly. Ramshorn produce eggs and you will have more than you could want fairly quickly. As long as there is food these snails will reproduce.