Dear’, and you don’t need to start the thing off with someone’s name. A formal email can be started with Hello, whilst if you know the person then you can just behave as if you are talking to them face to face).
Paragraph 1: Most business emails are short, so you might only need one sentence but we would always advise at least two so that you can sign off properly. Get most of your information out in your first paragraph. Make the sentences as brief as possible, without seeming curt.
Paragraph 2: The conclusion. Here, you should thank the recipient for taking the time to read the email, and mention that you are looking forward to hearing back from them.