Paragraph 1: Traditionally used to catch up and ask your correspondent how they are, and what is happening in their life. Again, this is not a strict rule, but a guide.
Paragraph 2: This section of the letter should focus on the message of your letter, and this can run for as many paragraphs as you like it to. It’s a casual letter, so this section is entirely up to you.
Paragraph 3: Conclusion. This conclusion need not sum up the rest of the letter in the manner that a business letter might. You might be better served by indicating that you are looking forward to seeing the person, or by giving another personal comment of a similar nature.
Here you can use whatever feels best – Best Wishes, Regards, With Love, etc.