What duties are involved? - It depends on what the client will want and what software they use. They may want payroll, VAT returns etc as well as book-keeping.
What type of customer? - Usually small businesses and self-employed individuals will look for a book-keeper.
Charges? - Depends on where you are based, and the level of book-keeping you will provide (basic book-keeping, management accounts etc)
It is good to keep up to date with tax and general law, but not essential.
I am a tax consultant and do tax returns and final accounts, but do not generally offer book-keeping services myself (although I do some). I have a few book-keepers that I reccommend to clients depending on where they are based.
Where are you based?
If you are interested, PM me and we can arrange a meeting if you are in Dublin or Wicklow.