When in doubt, just say "I have"-- "I have got" is repetitive, unnecessary, and I ddoooon't think it's actually grammatically correct...I COULD be wrong on that, though. But "I've got" is very commonly used in informal conversation. "I have GOT" can also be used for emphasis though, as Eliot used in the sentence "I've got to leave," often you'll hear someone say "I have GOT to leave now." Another example, in Batman Begins when Batman goes wooshing by in his tankmobile, Gordon says "I('ve) gotta get me one of those..." Hope that wasn't more confusing than it was helpful :)

They are interchangeable. #1. I have a book. I've got a book. #2. I have to leave. I've got to leave. .....but..... #3. I'm having fun. (You can't use have got here)

when explaining the meaning of occupying something, we can use both in formal english , we can say "i have sth." or "I haven't sth." it doesn't exist in american english , in informal english it can be "i have got sth."