Is there any difference between saying "remain patient" and "stay patient"?

Give me some examples of how "in the early days" is used in a sentence!

Sure thing! It usually references when something began or started in the past. Ex: In the early days of cinema, people used to dress up to go watch films. Ex: No one thought our cell phones would end up being this small in the early days of tech. Ex: In the early days of our project, we struggled a lot with determining our main goal. Ex: We thought our business would not succeed in the early days.

Is there any difference between "have forever been" and "have been forever"

No, there is no difference in meaning between "have forever been" and "have been forever", except that "have been forever" may be a little less commonly used. A more common structure of this sentence would be "could have been changed forever". Since "forever" is an adverb in this sentence, it can be placed in many different parts of the sentence without changing the meaning, such as at the beginning or end of the sentence, after an auxiliary verb, or before the main verb.

Is there any difference between saying "remain patient" and "stay patient"?

There is no significant difference! "Remain" and "stay" are synonyms, so using either of them is fine. The only difference might be that "remain" is slightly more formal in tone. Ex: Remain vigilant, our enemies are close by. Ex: Stay safe, see you next time!

Is there much difference in tone between "not really" and "no"?

I'd say "not really" is a softer version of "no." It's more gentle. But, it also depends on the tone you use when you say "no." Ex: No! You can't use my umbrella. Go away, Jerry! Ex: A ~ Do you like ice cream? B ~ Not really, no.

What does "alight" mean? Is it a common word?

The term "alight" is a common word and has a few different meanings. Here it is being used to mean shining brightly, or brightly lit up. This word is probably used in this song because of the many references to stars. Ex: The sky was alight with hundreds of fireworks. Ex: The room was alight with candles.