Quote Originally Posted by Melichoir View Post
Though I do wonder if you were to purchase additional retainers, does that retainer limit increase across all alts?
As somebody with additional retainers and an alt: yes.

They aren't character specific, they are account-wide, so if you buy let's say 2 additional retainers, and have 1 main character and 1 alt, it means that you can have access to 8 retainers in amount (2 free and 2 paid for each).