You can't put the male and female together unless they are breeding, and that's only during the breeding process.
Sometimes you can have multiple females in a tank. Depends on their personality and if you've enough room and hiding spaces, plants, etc.
Snails may or may not work with bettas. Again, it depends on the betta's personality. Some will ignore the snail. Some will try and eat the tentacles since they look like little worms. My betta kept my snail pinned down in the corner and I had to rehome the snail. Failed experiment. Though now I have two 5 gallon tanks, one for each!