I love hiking. I think you’ve got a decent start with what you’ve written already. I would advise getting familiar with navigating yourself with a map and compass, a lot of places don’t have phone signal so at a minimum download your map and make sure you’ve got the battery to last the trip and some extra. I definitely agree with your thoughts about carrying more water than you think you’ll need, generally water will be the heaviest thing will carry but one of the most important.
The state of your mental health is not necessarily your fault, but it is your responsibility. It’s ok to be having a bad day, week, or year but it’s not ok to hurt other people because of that.