>> Oh, I forgot to mention Beltane also! Thank you for adding it. c: <<

Glad I could help. I'm Pagan so I figured Beltane should be in there.

>> I've looked through the lists on the card maker, but I'd also like to submit my own. How would I go about doing that? <<

You can contact magistrate here:
http://magistrate.dreamwidth.org/34518.html

>> (Oh, and I can definitely come up with a spring/seasonal list for the fest, too. I was planning on that.) <<

That would be awesome. If you look at previous fests, you'll see that some hosts like to make modular lists so that people can mix and match as desired. Frex, you might make a Pagan list and a Spring list.