Maddy! You keep changing your mind, doncha? I thought you wanted to keep apple snails??
I think, but I'm not sure, that my betta has sucked a few nerites out of their shells. I have found a couple empty shells, not sure if the snails died and then were eaten, but I don't think so. But for the most part my betta leaves them alone.
I wouldn't keep a guppy with a betta either. They might get along now, but I wouldn't count on it. Bettas go after fish that look similar to themselves, brightly colored fish with flowing fins. I would guess that some day, unless you have a large tank with lots of hiding places, you are going to wake up to an eaten guppy.
I keep my betta at 80F also, siva. They are in the same tank with ADFs and they all seem to enjoy the warmer temps.