Ja to bym napisał tak:
I am writing to you because I am interested in the summer English course. I found your adverisement in "Daily" newspaper yesterday and I liked it a lot (nie very like). Could you send me more details about this? I wonder how long does the course take and how many hours of teaching does the price include. I would like to know what places are you planning to visit. If it is possible I would like to invite my friends.
Thank you for your help and your time.
I look forward to your reply.
Yours faithfully
XYZ
Nie gwarantuję, że jest bezbłędnie.