Good luck, Frances! What made you choose an Ultra as your first big challenge? You may want to set smaller goals along the way, just to keep the momentum up. Looking forward to reading more about your adventures.
I like to have music for longer runs to figh monotony, evening runs (with caution!) when I can't see much and need some entertainment. I have also used music during the final 10k of a marathon where I needed the extra energy coming from a good beat. I do not use music for forest/trail runs, I see no need as I want to fully immerse myself in nature.