It'll take a while for us to heal and it shouldn't be underestimated how great it is that you're sober and embarking on this new life!
I had a breakdown last year and was working in a very low-stress job and it was a blessing for me. It allowed me to go in at a set time, have set breaks and leave at the same time everyday. I knew what I was doing, nothing unexpected happened and it gave me that space to sort myself out. If you need to do the same in your job, turn up, work, go home, and that helps keep you sober, then for now, it might be what you need.
The fact that you have an opportunity to have more responsibility at work on this project is kind of exciting, but if you can't take it on right now, that's okay too.
Don't feel bad about the progress you're making. You're working and you've embarked on this new, sober life, this is great!