Puffer questions...

I am *SO* sick of pond snails! I've got assassin snails but they aren't nearly keeping up so I'm thinking of getting a couple of puffers that I can rotate around.

Questions:

Will they go after my shrimp? (amanos, cherries and snowballs)
Will they bother the large snails? (nerites of various kinds and assassins)
Will they harass my little fish? (mostly danios of one sort or another)
Any special water perameters?

Thanks!