As regards studying for the Citizenship Test
this book is recommended.
Newpost, as regards your no. 4, "Wait for a while to get the naturalisation certificate", what you will hope to get is a letter saying your application is successful. You will then need to attend a Citizenship Ceremony during which you will be handed your Certificate of Naturalisation.
Your no. 5, "Apply for the passport in the post office" .... as from a date later this year all first-time applicants for British Passports will need to attend in person to apply for their first British Passport. It will no longer be possible for first applications to be submitted over the counter at a Post Office.
By the time you have got the Citizenship Test out of the way this new provision about first passport applications will probably be in force.