"Go meta" refers to the action of doing things in a metaphysical manner, that is to say, in a way that considers the effects of one's actions, instead of simply acting them out. "Meta", in a broad sense, means "self-referential", examining the self and the self's actions while at the same time being that self and performing those actions.
It might help to thing of it as going "plus one level above" and acting as if you were watching yourself doing the action.
In this case, "normal" would be to simply say things that may cause discomfort or be manipulative in nature. To go "one level above", you would openly acknowledge that your actions may have said effects, and yet still act them out.
To "go meta" in a game, you would not just perform things that would get you a good score, but also things "above the game, only visible by an existence beyond the game (the player)", such as completing achievements. These achievements have no effect in the game, but are part of the entire experience for the player.
Best Answer
Not too many years ago I would have advised you against using the term "homie", as it is connected to the vernacular of a particular ethnic group, and you wouldn't want to sound like you were mocking them by using it incorrectly. Nowadays the word is much more common, so, given that Dicaprio can use it without causing offense, you might sound out-of-touch, but not actually offend anyone.
Hopefully. It can still be used in a racist manner, so you should still use good judgement.
The etymology of "homie" is unclear, but since it's most commonly associated with Latino slang I always assumed that it derived from the Spanish hombre, which means "man" but is used to refer to any male who you are close to or at least friendly with. Wikipedia gives other possible explanations.
The meaning is similar to saying someone is a "buddy", but the actual nature of the relationship can vary from person to person. Dicaprio doesn't literally mean that Winslet is from his home town (he is from California and she is from England) so his meaning is clearly that she is a "close friend". Meanwhile, someone else might use "homie" to mean "someone I would trust with my life".
Meanwhile, someone else might use "homie" in a scornful way, to indicate animosity. You will just have to judge from context.