Guild Wars 2

How many bank guilds could one person create/belong to?

Definition: Bank Guild is a single member guild typically used as an additional storage facility.

Reason: Just got a good guild name that I could “reserve” then maybe expand membership in the future.

You’re only able to create one guild at a time, if you’re already in one you created then you don’t get the option to start another. So the answer would seem to be just 1.

But I’m not sure if you can have full leadership permissions in 2 or more guilds, or what happens if someone else creates a guild, adds you as the only other member, gives you full leadership permissions and then leaves.

You can be in up to 5 guilds at one time and you can be a leader in all of them. I have 2 bank guilds, which of course I am the leader of.
To create a new guild, just stop representing whatever guild you are a member of. You can then make a new one.