I agree fully with #1 and #2. Wise advice not to be so impulsive.

But as for #3, I guess if a person is so fed up with his current employer, then it's also just as well to apply for any job that he can qualify for, then get out first, as fast as possible. This is better for mental health! Applying to many many jobs also means better chance of securing one and getting out of current situation quickly.

#4 very true. In fact, don't tell anyone at work or even update your social media status etc. until a month or more after new job is secure.