it depends on the type of snails. if you are looking to breed pond snails for a food source then you probably won't need a heater. if it's ramshorns or briggs (apple snails) then you definitely want a heater and the temp should be 76 to 78.
briggs will need the water level dropped down a couple inches from the top of the tank so that they don't go wandering out of the tank looking for a place to lay eggs. i would have only one male and one female in a 10 gallon, since just one egg clutch can yield up to 200 babies approx.
ramshorns lay their eggs in circular jelly-like patches all over the tank underwater.
yes, definitely will need a filter no matter what type of snail it is. i would reccomend an Aquaclear hob rated for a 20 gallon tank, and put a pre-filter sponge on the intake tube so that baby snails don't go for an impeller ride, lol.
things like substrate, decor, plants, etc is purely personal preference (phew, don't try saying that ten times fast, hahaha!).
here is a 10 gallon i had set up a while back for brigg breeding. it worked really well! (heater wasn't necessary as my apartment was always really warm, and i didn't have a pre-filter sponge on it, but not too many baby briggs got into the filter anyway)
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