I did a few weeks off coffee couple of months ago, it is indeed one of the worst ones. Nicotine for me was purely mental with very few physical symptoms, caffeine was horrendous. Then a helpful soul on here informed me I hadn't really detoxed off it, as it apparently it takes about a month to fully work out of our system!

Good luck with your new habits. And remember if you do have a day where you 'fail' with one of them it's not a failure, stopping for a week is a giant improvement on everyday.