Hello,  Ronnie; , 

I would love to spend my summer holidays with you, because I really adore the beach, the sea and the town where you live. As far as I’m concerned, I don’t have  got  anything better to do, therefore, we could spend one month of the summer together.

I would prefer  to suit  July, because I’m going to go abroad with my parents and sister. So, unless you have any  problem  concern, I will go to your town on 1st of July.

It doesn’t matter which room you give me. Although,  if  I think it  better,  best   if  I will choose your spare room, because your sister might get angry if she discovers  that I was in her studio.

Talking from experience, I won’t spend a lot of time on the beach, because  while  I love the sea,  nut  I really hate the sand. Therefore, we could visit interesting places or play sports.

Love,

Álvaro.

----------

This is a very good letter. Well done!

Normally, when we introduce a person's name, we separate the name with a comma:

This is my sister, Kate.

My sister, Kate, is a high school student.

Thanks, Kate!

However, the start of a letter is an exception.

 Dear, Kate;  (this is wrong)

 Dear Kate,   (this is correct)