Learn English – “walks” or “walked” or “will walk”

As other answers have indicated, the future progressive, as the term implies, can place emphasis on the ongoing nature of the future event. In such contexts the future simple is not correct:

This time tomorrow I'll be lying (*I'll lie) on the beach.

Sorry, I won't be able to make it. I'll be playing (*I'll play) tennis with Mike.

However, this is not the only use of the future progressive. It is often used when there is no particular focus on the ongoing nature of the future event:

You'll be hearing from my lawyer.

She'll be starting school soon, won't she?

In such cases, the future simple is also possible:

You'll hear from my lawyer.

She'll start school soon, won't she?

although, to my ears at least, these are very slightly less natural.

Now we come to the OP's examples, both of which are perfectly normal ways to tell someone of your friend's holiday plans.

There is possibly one small semantic difference, however. Namely, that the progressive form could carry with it the implication that the visit is part of an arrangement, whereas the future simple is a simple statement of fact. As such the future progressive parallels the use of the present progressive to express arranged future events:

I'm playing tennis with Mike tomorrow.

I'm visiting my grandparents at the weekend.

She's visiting Chichen Itza next week.

But in Fumblefinger's term, this is "armchair rationalisation", a process that no native speaker consciously goes through in advance of what they say in day-to-day conversation.

In summary, the OP's two sentences are virtually equivalent, but there are other contexts where only the future continuous is possible, or where it may sound a little more natural than the future simple.

Consider there's your colleague named Jack. One bad day, he has been sacked. In this context, I'll try to answer your questions.

You asked the differences. Here are they.

You are informed (-sense#1) of something ~ You are informed of Jack's sacking.

Either someone told you or you got this information from somewhere (maybe, an email or something for example). Point to note: You did not do any effort to know this piece of news.

You come to know something ~ You come to know that Jack has been sacked

This is quite similar to the above one but when you inform someone, it's official and when you come to know something, it could be through gossip, general talk or things the like. Point to note: You may or may not do any effort for this. This may come as your efforts, coincidence (employees were talking about it and suddenly you came) or luck. In other words, say, you enter into gossip that has been already going on and there, the topic of Jack's sacking comes (with no effort, you came to know this news) or you toss a topic of current sacking in the company and someone tells you that Jack has been sacked (you made some efforts to know who all are been sacked).

And lastly,

You are aware of something ~ You are aware of Jack's sacking

This means Jack's sacking is probably declared and well known. You know or realize this news (sense #1, sense #2 is also possible but then it'll be in a different context) and you are pretty well aware of it. In this context, being aware means the person who's talking to you is probably confirmed that Jack's sacking is not a secret to you anymore. And again, you are aware of it.

Now the second question:

No, they are not interchangeable all the time.

You cannot be aware of something unless that something is being informed to you. Check the example there: "I don't think people are really aware of just how much it costs." True, you have to inform them to make them aware.

Likewise, if you come to know something, it does not necessarily mean that someone informed you. The knowledge of that something has come to you because of your efforts, luck or coincidence.

Hope this helps.