Its a job that requires you to be a certain age, therefore Birth Certificate is like the first thing on the list. Especially for proving your identity.
When it comes to the actual list, it can be tedious, but I would advise getting to the physical and passing that first. Don't think ahead to phases that you haven't reached yet. You will have enough time between the Physical and Investigation to come up with what you need. And even then you can be granted more time.
My advice for those on the new list would be to work on fitness. It'll help for the physical, medical(weight), and the PT in the academy.