I know the rating decreases for WA, but does it decrease for TLE in Cook-Off, lunchtime or long challenge?
It counts the same as WA.
So if I submit multiple TLEs, will I get multiple rating loss?
No , thats not how it works
All things except AC are counted as WA. Overall will your rating decrease or not depends upon your rank and previous rating.
So there is no difference between not solving and WA? I mean, if I solved only 1 question in this cookoff, and on the other 4 I got WA, will I get the same rank as when if I had solved only 1, and the rest were un-attempted?
In simple words, is there a score/rating/rank penalty for WA?
No. You will get the same rating if you solved one question, and the rest went unattempted.
Yeah, penalty is only counted after AC in that question. If you have 4 WA in any ques and didn’t get AC then penalty will not be added