I'd focus on getting the PPL out of the way; I assume you have passed all of your PPL exams.
You'll find the PPL studies are a good grounding for the start of the ATPLs. I often founf myself leafing through the PPL books when doing the ATPLs, since they often were slightly better at explaining complex things.
You'll want to avoid having to purchase the books twice. If you do spend cash on books, try and get ones for the school you'll be going to.