1)enough is enough.
5)so be it.
6)By the way.
Angelic, you have chosen phrases that tend to be associated with conversations that are not always agreeable ones. Really they are mostly self explanatory.
Would be said when you can’t take any more of the noise/argument/situation.
2)Many, many occasions when this would be used.Too many to list.
3)Similar to (1). Just about to leave. Just about to phone/call/write/tell you.
4)Only just arrived. Only just made it to the concert. Only just heard the news.
As the closing comment to an argument or heated discussion. So be it!
Remembering something that you had forgotten to say. Oh, by the way…
7)Again, a closing comment … anyway, it doesn’t really matter.