1. Good to see you!
2. Good to meet you!
3. Good to meet you again!
[Can we use #2 only when we meet someone for the first time? Can we use #1 when we meet someone again? Can't we use #1 when we meet someone for the first time? What is the difference among them?]
2 is for when you meet someone for the first time, yes.
3 is used when you meet someone you already know.
1 can be used for either purpose.