The reference book contains content from the core book, so it's purely optional!
For the asset deck, you have a couple of options:
1) Just copy down the ability text from your character's asset cards. Most of the abilities are fairly simple, and you start with a limited number.
2) Use a digital app to track your assets. Depending on how much you want to go digital versus analog, you can do just about everything on an app. Check out your options here: https://tomkinpress.com/pages/community-resources. Or use the app for some things and your physical journal for others.
Hope that helps! Also feel free to join our Discord. Folks there always have good advice: https://discord.gg/8bRuZwK