Thanks for your letter, it was great to hear from you. I'm sorry I haven't written for months, but I had some personal problems.
It's really good news that you've passed your last exam. Congratulations!
Thank you so much for your invitation to stay with you for a week in July, I'd love to come. I know that you have a wonderful beach near your house, and I'll really enjoy spending some time there. I expect that the weather will be hot, so I hope we can go swimming.
You indicated that I don't need to bring much with me so should I pack casual or formal clothes?
I'm looking forward to seeing you in July and to having a great time.
Thanks again for the invitation.
All the best, Michael