HI Scarlett! First, I highly recommend that you do commit to running the Tinkerbell Half Marathon! I ran it last year and it was a great race! You can sign up for an email reminder for when registration opens on the
Tinkerbell Half website. You definitely want to sign up quickly as it filled up fast last year!
As for the 5K, it is also a really fun race! If I do the 5K before the half marathon, I like to take it slowly and use it as a fun walk with my family. Doing both is a great way to get the whole race weekend experience.
I asked the runDisney staff about a discount for annual passholder's and was told that there is not one currently. Of course, that is always subject to change, so you should keep checking back on the half marathon website details page.
Please let me know if I can help with anything else!!