Blizzard has provided additional details on the Wow Classic account character limits.
Community manager Kaivax provided clarification on the character limits in World of Warcraft’s vanilla server option following a question on the official WoW forums. Interesting to note is that there won’t be an overlap with the character limits for retail (i.e. Battle for Azeroth) World of Warcraft accounts. Players will be able to have up to 50 Battle for Azeroth characters and up to 50 WoW Classic characters at the same time.
The following characters limits will apply in Classic:
A maximum of 10 characters per WoW Classic realmA maximum of 50 characters across all of the WoW Classic realms in your regionOnly one faction per realm on PvP realmsNo overlap or regard with the character limits in Battle for AzerothWorld of Warcraft: Classic is slated for a release this summer. Blizzard's Vanilla server option will be based on World of Warcraft patch 1.12 'Drums of War'.