I need some help on appearing very professional on my first freelance project. How / What should you do to achieve this?

Background: I started as a full time web developer 18 months ago, two promotions later I am now a senior software engineer. I've never had any problems with designing / developing / coding a complicated system.

I thought I could use some help for Christmas and I started bidding for a project and now I have one - from a very reputable lawyers association in London. I have no problem dealing with the actual implementation of the system, but I have no idea how to appear professional throughout the whole process.

About the project: This lawyers association are starting a distant training courses and in addition to having a website to show off all their clients etc, they want a students area where their students would log in, download course materials allocated to them etc.. and an admin section where they assign courses to students / create new ones / upload materials etc..

Questions breakdown:

1) How should I start with the requirement gathering? Is using scrum a good idea, or should I use something like Volere Template - and what should I do with it? should I submit a copy to the client etc..

2) How often should I meet the client? Would once a fortnight would be good?

3) What are the processes / protocols that I need to follow so that they would be satisfied with me and think that I am very professional

4) How much should I charge for the product?

5) How should I get a quote / contract / receipt for the whole project?

6) What are the steps that professional freelancers go through, during the life cycle of a project?

My Research so far

Looking at How much should I charge doesn't help.. I live in London, zone 1, though I have no idea how much a project of this size would cost. Help on this would be appreciated.

How to be professional articles talks about the work / time management etc and not the actual process, what would real people do etc.. it's like academia theory, but not practical.

If this needs revising, please let me know, do not close it because of whatever reason, I will edit the question or details to fit the needs.

Thanks for reading a lengthy question.