Is there a way to adjust the size so it fits the content I have in the page, or do I have to adjust the page size manually? Thanks
Negative, you will have to adjust the page size (file> document setup) or you could just bleed your image of the edges?
If you change the size of the page manually (File > Document Setup), it will change the size of all pages, not just this page. I'm going to approach this as if you are a super beginner (no problem with that) and you're dropping everything in as a single illustrator file. Please correct me if I'm wrong.
Here are two things I'd advise:
Best of luck!
when using the Shift P page tool you can hold down Option Alt key when clicking on the box to resize and it will stay the size you edited it to be.