You can offer as many fandoms as you like and will just get one assignment.

For each fandom that you request or offer to write, you can specify one or several characters or "any" if you are open to any characters, and that will affect how the assignments get assigned. If you say "any" in your offer to write, you might well get a request for a pairing you wouldn't have thought of writing.

Filling out the form is a little tricky but the fest is all kinds of awesome. I think you'll have a good time if you join in.