How is my informal letter?

You basic structure is good...you just need to clean up some grammatical and syntax issues. Re-read out loud...doing this you will find where it's not flowing right. For example: "Everything's good in Italy?", structurally that sentence is a statement, not a question. Everything's is a contraction of "everything is". So, you would need to reword it to say "Everything is going good in Italy?" or "How are things in Italy?". Just go from there...you'll figure it out!