Didn't know you were the DM. :neutral_face:
You can make your character sheet just in case. Can't say for sure when we might end up needing a substitute, for example after someone dies.
I still have no idea how the people behave themselves, so if there are people who dick around way too much, then I'll just give them the boot and would introduce your char at the next cornerstone of the campaign.
So yeah, either someone dies, they leave or they get kicked out. Each case would open up a slot for you.
EDIT: Actually, since we have not even started yet, I'll do it another way. I'll invite you to the conversation and if your character and it's backstory impresses me, I'll just straight up switch you into the team, and kick someone else out.