Custom Usernames - How would I save a list of names so that players don't share names?

Explaination

I'm trying to make a system where players can have custom individual names. It's a huge hassle that at first doesn't seem necessary, because players can use their own usernames, right? But here, I want to be able to later on let players have multiple characters that have individual Identities(including their factions/relations/et cetera).

So at first - I was pretty much going to do something like this.

Example 1

NameCollection = {"Teemo","Teemo2"}
DataStore = game:GetService("DataStoreService"):GetDataStore("CharacterNames") 

for index,value in pairs (NameCollection) do
    DataStore:UpdateAsync(index, function() return value end) 
end 

Which I just scrapped after a couple minutes of the idea because if players were to have multiple characters, a table would be GIGANTIC. I'm mostly scared of how inefficient it would be.

So what I'm asking mostly is - how would I save a list of players, which is saved across a datastore that can be accessed by every server? It can be a table-related method, but If anyone has any ideas please say!