1) Does it sound odd to say to a flight attendant "Are we going to get there soon?" or "Will it be much longer before we get there?"

Not at all. Those are good questions to ask.

"Turn the tv down a little" is fine, it's used very casually. For the later sentences, I would switch it to - "You've turned it up too much," "You hardly turned it up," "you barely turned it up." ------ "too little" sounds very awkward, and I would switch "the TV" simply to "it." 

3) Should I say "How do we go back home? In fact/Actually , how did we EVEN get here AT ALL?" or "In fact/Actually, how did we EVER get here AT ALL?

That's fine, "how do we get back home" is  a little better. All the other forms of the sentences you're using are fine, it really depends on how you're trying to portray your message. I would go with "In fact, how did we even get here at all." ---- I wouldn't use "ever" here. 

4) Does it sound odd to say "Scientists may have years and years pass without them publishing anything"?

A bit, try - "It could/may take years for scientists to ever publish anything," or (trying to make it sound more like your original statement) "scientists could have years pass by without them publishing anything"