What does "vacay" mean? And do you use "vacay" for real?

Could you give me some expressions that can be used instead of "free of charge"?

Some synonyms for "free of charge" are "free" "complimentary" and "at no cost".

Is "whatever" a general expression? When do you use it? Could you give me some examples?

"Whatever" has a variety of different meanings depending on the context. Here, "whatever" is used to mean "anything" or "anything you want". This is one of the most common uses of this word. Ex: Take whatever you want! Ex: We can do whatever. "Whatever" can also be used to mean "regardless" or "no matter what", expressing that something is unimportant. Ex: Whatever grade you get, we still know you're smart. Ex: Whatever the weather looks like, we're still going! "Whatever" is also used sometimes to express disinterest or to show that you don't care about something. This use of the word is a little bit rude. Ex: "I bought you some ice cream!" "Whatever."

What does "dish" refer to in this context?

In this context, "dish" is referring to the telescope mentioned previously. She says "dish" instead of "Aperture Spherical Telescope" since the shape of it is like a "dish". It's similar to a satellite on your house for a T.V- you call that a "dish". Ex: The T.V dish fell during the storm. Ex: The satellite dish was not working.

How can I interpret "way too fly" part? Is it something like slang?

Yes, "way too fly" is a slang phrase that means the same thing as "way too cool". "Fly" in this context means the same thing as cool, awesome, or amazing. It is a phrase often used in hip-hop music. Ex: I'm feelin' so fly like a G6.

Does the phrase "play along" have a negative nuance? If I say "I will play along with him to win.", does that mean I will cooperate with him unwillingly?

Sometimes it can, but not in every scenario. In this scenario, it does have a negative nuance. Moana tells us that she will make herself happy by following the rules of her tribe. However, she knows that this won't make her happy, so it has a negative connotation. The sentence you asked about seems like a negative nuance. It would just depend on how it's said and the circumstances of why it's being said. From reading your example sentence, it sounds like it has a negative nuance and does mean I will cooperate with him unwillingly to win something. It can be challenging to pinpoint what "play along" phrases have positive connotations and which ones have negative connotations. I will give a couple of easy examples to give you an idea of what "play along" would look like with a positive nuance and a negative nuance. Ex: Fine, he wants to do this, then I'll play along. => negative nuance. Using "fine" is an indicator that the speaker is annoyed. Ex: Ooh, that sounds fun! I'll play along! => positive nuance. Using "ooh" shows us that the speaker is excited about something.