#1 is good, you could also say "I was sitting by myself". #2 "It was lurking." or "It had a sense of foreboding" - I think that fits the general meaning? #3 "He wants to organize a meet-up." This is the only thing I can imagine "knees-up" means, I've never heard this before... #4 "The temperature was declining." or also "The temperature was falling." The last one is probably more natural. Pretty close on this one though :)

Agree with all of the above, but for #4 I would say "It's getting colder outside."