A psychiatrist once told me that all anxiety is uncertainity in one form or another. So when you feel anxious you can ask yourself what is uncertain about the situation you are in that might be causing the anxiety, or what feelings of uncertainity do you have if the uncertainities are fears rather than an actual uncertainity.
It doesn't make the anxiety go away, but it helps you to observe it rather than being overwhelmed by it. Also, anxiety is natural.
My advice about panic attacks is not to try too hard to avoid them, because trying not to be anxious can create a kind of avoidant behaviour that usually makes the anxiety worse and leads to more panic attacks. Better to observe the physical sensations, note what the anxiety is about, and practice some grounding exercises until it passes. Accept that it will happen, and learn how to get through. Over time as you accept yourself more and more and try to control less and less, the panic attacks should also reduce. (That's my theory based on my experience anyways.)
You are on the right path. You are doing your best. It is enough. Try not to label things as failures, just do that cliched thing of learning from outcomes. The pain of things that have not worked out is enough for you to bear without also beating yourself up about them. Especially now that you are trying so very hard to go in another direction. It really is enough. The old John doesn't exist anymore to feel bad about, and he was just a person struggling anyway so he shouldn't have to feel bad at all actually. But now there is just this John, the one reading right this second. He is doing damn good with life, because the hardest thing in the world is being emotionally honest with yourself instead of telling yourself stories in your head about who you are. This John is living
Mindfulness is good. Anything from a MBSR course (Mindfulness Based Stress Reduction) is good, the main guy who developed it is Jon Kabat Zinn.