We don't actually have a launch date for the Cataclysm event. I believe the current Freeplay events are breadcrumbs, since no special currency is dropping.
Many of the new cosmetics will be available for direct purchase with the event currency. New gear, weapons and such will be available in chests purchasable with the event currency. The chests will rotate throughout the week, ie weapons one day, melee weapons the next, and then new gear, etc.
You can earn the event currency by participating in the special freeplay events, completing event challenges, incuding dailys, weeklys and one-off, and completing runs of the cataclysm itself.
As far as I know the featured store is entirely separate from the event store.