The easiest way I've found to do it is to pick up some Excedrin (or the generic equivalent). It's basically just aspirin and caffeine. Go as long as you can in the day til you start getting a headache, then take 2 pills. Do that for a week. The second week, take 1 pill. By the end of the second week, you won't even need the 1 pill, you just won't get the headaches.

Depends each time. First time I quit it was a week of headaches and two more weeks of sluggishness. Second time it was a day or two of headaches and a week of sluggishness.

Second time around I did just accept that I was going to take paracetamol by default (so on a regimen and not reactive to pain) to take the edge off the headaches though so that could've helped.

I went cold turkey and it was very unpleasant. I cut it down gradually and it worked for me. Good luck!

Use green tea (you can make iced tea with it if you don't like the flavor) to get off coffee. It provides just enough caffeine to prevent withdrawal. Then after three days you can go cold turkey. This method has worked for me several times when I had a massive coffee habit and had to reset for a while. I am older now I have one or two in the morning and usually tea in the afternoon.