SS, great to hear your son is still moving forward and embracing his recovery. Kudos to him!
The answer to the resentment question for me is, yes and no. But the situation in which I have moved passed my resentments was similar to the one you are dealing with. My son's dad was abusive- verbally and physically. I left him when my son was young. Over the years he never helped with my son, financially or otherwise. I felt resentments towards him and I was intimidated to be in the same room with him for a long time.
I think the resentments went away when I began to think of my time supporting and nurturing my son as a gift --for myself and my son. Today I am grateful his dad wasn't around very much because that meant my son didn't have to grow up around his anger and meanness. I'm also proud that I was able to be there for my boy and I did it on my own. His dad now wonders why S. doesn't call him. I think that is kind of his own self-induced punishment. Even his parents have told me they are thankful S. had me and are disappointed in their son.
Just my experience. I haven't worked my fourth step yet, so I don't have any experience with it. But it does sound like a good, solid plan for you. I have heard that many good things that come from working and reworking the steps.