10 + 2 = 12
I think he does mean 12 PER
server. As sub you can create 12 characters in, say, The Progenitor server and another 12 in Red Eclipse and so on.
To OP, I was in the same spot you were a month ago and when I went sub, considered deleting one of my original characters coz I didn't like the way I built her looks, but then thought otherwise. As others here were saying, you'll never know when you feel like playing that char again. Only consider deleting if you fill up the 12 slots in your server and you want to keep your Legacy links or share loot and credits between those 12 chars.