Can you journal about more than one topic in a journal? Of course!
You can divide your new book into different mainstay topics. For instance, if you know you want a section on inspirational quotes, another section that plans your day, and another on how you are feeling, then you can section off a journal into three even parts and place a book mark, post-it note, tag, or other marker on the start of each section so that you can get to it easily.
You can journal about more than one topic on the same page. This is where headers will come in handy. Draw spaces for the different topics on the page and write about them in their designated spaces.
Play around with formatting to see what works for you. As always, have fun in the discovery process. Understand that even those of us who have journaled for decades change things from time to time. Do not feel obligated to stick with one format if it does not work for your needs.
Peace,
Deborah