We know that there will be three, based on Fire Emblem Fates, Fire Emblem: Shadow Dragon, and Fire Emblem Awakening, which can be purchased in $8.99 single packs or together in a $19.99 season pass.
With Fire Emblem Warriors, players will be able to purchase add-ons that bring new playable characters, history maps, costumes, support conversations, and weapons.
These Fire Emblem Warriors Australian eShop listings also clarify some information about other pack contents.
The first Fire Emblem Warriors DLC back, based on Fates, will be released in December 2017 and add Azura, Niles, and Oboro as playable characters.