1. Does a Book of Shadows have to be leather bound? If not could I use a regular blank bound book who's cover isn't leather?
A Book of Shadows can be anything, it could be a three ring binder, a spiral notepad, a lether bound book, it can even be typed on the computer [personally i'm not a fan of your BoS being a document, but it's up to you] whatever you feel works, use it.
2. If a spell calls for a dream journal, can you use your Book of Shadows?
whatever you feel goes into it, go into it. in my opinion though, you should have a dream journal and a Book of Shadows, because of space. your BoS can have dream interpretations, but the actual dreams [just due to space] should have their own book.
3. Does anyone know of a good astrological calendar I could use?
a quick google search can find a astrological calendar. my phone has a free app that's the map of the night sky. which hemisphere are you in?