Dear Ken,

Many thanks for your letter. Your offer sounds very good, but I need more information about the beginners courses. {As a copyeditor, I wouldn’t change this because it’s a descriptive phrase. However, "beginner’s course" would be widely accepted.}  

First of all, how many weekends do I need to get the certificate? {This is OK, but "how many weekends would it take to get the certificate?" might be better.} As you know, I've never sailed before, so I don't know a lot about it. Could you tell me what the RYA2 certificate is, exactly?

Also, I would like to know if it's necessary to be a good swimmer. I learnt {"learned" is more common in American English} it when I was a child. However, I'm not sure if I am skilled enough for the course.

Finally, I wanted to ask you some questions about accommodations there. Is it expensive? {This is ok, but it’s better to ask, "Are hotels expensive?" for clarification} If so, would you mind if I stayed at your house with you? I can't afford to stay in an expensive hotel and also pay the course fee.

Hope to hear from you soon.

Best wishes,

Ivan