I am planing to start an online dating business from UK (but wishing to offer service worldwide)

Everything is in the initial planing state. First of all, I like to know the legal issues regarding this. The following questions are arising in my mind:

(1) Which is good, operating as a sole trader or as a limited company?
(2) Do I have to get permission before start the business?
(3) Do I have to pay tax to the UK government for the customers outsite UK?

Thank you.