What's the difference befween 'wanna' and 'want to'?

Does it mean same if I say "I'm gonna be gone about a week" instead of "I'm gonna be gone for a week"?

If you say "I'm gonna be gone about a week", this is different than "I'm gonna be gone for a week", because "for" gives a specific duration of time, meaning that it is going to be exactly one week that he is gone. In this case, however, he actually says "I'm gonna be gone for like a week", which has the same meaning as "about", since "like" in this case is an approximation. So "for like" means that it is going to be about a week that he is gone.

I thought "spice" is only used in food. Does "spice" mean something else, or is it newly defined in this movie?

Yes, this is a very unusual way of using the word "spice." I haven't seen the movie and the trailer does not provide too much information, so we can just assume that "spice" means "particles" or some other visible matter in the air. You wouldn't normally use spice in this way. It's either used to describe the seasonings used in cooking, or to describe people who have exciting or energetic personalities. Ex: I love Martha's personality. She has a lot of spice. Ex: I think I put too many spices in this soup. It tastes strange.

When can I use 'dawn on'?

'Dawn on' is used when you realize something new. It is more likely to be used in situations that you realize something new about something you'd already known.

What does he mean by leave money on the table? Is that an idiom?

Yes, to "leave money on the table" means to miss out on money that you could have gotten from a deal (as deals are made by sitting at a table). He's saying that people sometimes lose money or do not end up winning in a negotiation. Ex: I don't think that meeting went well. We left money on the table. Ex: I tell myself it's alright to leave money on the table sometimes. You can't win every round.

What does "succumb" mean here?

To "succumb" means to give in or submit to something often because it is forceful or overpowering. In this case, "succumb" is referring to giving in to a charm or a deceptive kindness because it is easy to do. Ex: Don't succumb to temptation. Resist it! Ex: He succumbed to his boss' orders.