Ability Capsule doesn't give a poke it's Hidden Ability. It only switches between the two (if that) normal Abilities.
After you beat battle 10, you get 2 BP per battle in Easy Singles in Maison, and then beating battle 20 alone will give you 20, at which ends the run and you can start it again, for 48 BP per run of Easy Singles.
Also, you CAN find Swift Swim Poliwag in any random Poliwag Horde battle in the Pokemon village; just take a Sweet Scent/Worry Seed Venusaur with a bunch of Leppa Berries if you can and just Sweet Scent, use Worry Seed on them until you find Swift Swim, and then kill the rest, catch it, and bam. HA Politoed material.