I am not sure if there is a real difference. However, it's not very common to say 'licit' in normal speech. In fact, I had to think for a moment about that word before I responded. Illicit, however, is used commonly when talking about drugs. It's a word you'll hear often on the news in the place of 'illegal'. "Two men were arrested today for possession of illicit drugs." "One person was arrested today after getting caught performing illicit activities." So in summary, in normal speech we would just say legal / illegal. But it's a bit more formal to say illicit, and rare to hear licit. Hope this helps!

I think that sounds fine. It's more poetic than everyday speech. In fact, a nice picnic does sound pretty nice about now, haha.

Regarding the differences between the first to sentences: "...advantage to..." vs "...advantage of..." I don't believe there is a rule or convention to follow to make the distinction more clear. In this case, I think that either sound fine. Don't take this as a rule, but to me, it feels as if I would say "...advantage to..." more often if I am stating the advantage, rather than asking. "Trust me, there are a lot of advantages to doing it this way. It's much easier." Compared to: "What are the advantages of doing it this way? Is it much easier?" Even still, you could still swap out 'of' and 'to' and it would be just fine in either case. Sentence three is incorrect. "It has" implies that there is a subject that these advantages belong to, however that's not the case. We are simply stating that these advantages exist. Sentence four is fine. Hope this helps!

Is sounds like he was going to say "So, in essence..." however, he was cut-off by the other speaker so his words were not clear. To be honest, I'm not 100% sure what the first man was trying to say (as a native speaker).

If I understand you correctly, then the word 'suspicious' can be used. Here are some sample sentences:

"Because this company's product is usually low quality, I am suspicious of their new product."
"Because my new cell phone broke so quickly, I am suspicious of how well it was built."

Hi there! Instead of making small corrections to each component, I will instead write your paragraph as I would have. I hope you can identify the differences and I hope it helps!

"Today is Thursday, and tomorrow is the weekend. Finally I can go home and rest. On Saturday some friends and I will play football and then have dinner, chatting about everything together. They are my best friends. Every time we meet we are all very happy - I can't wait! Writing a composition in English is very difficult for me. "