Your question is one I have been really grappling with recently, as well. Both my mother and a cousin have MS (not to mention other instances, such as witnessing the struggles a co-worker of mine went through when both of her children were diagnosed with MD), so this is very personal for me. Like, I almost got angry when people who had never met my mother before saw her at my wedding, which she had already been self-conscious about not being physically able to “dress up” for the way she would have liked, would ask me in hushed toned later “What’s wrong with her?” with this look of horror and pity. And I would explain that nothing is “wrong with her,” she has just been living with MS all of her adult life, but is a strong and active woman, as much as she can be. People like that are my heroes, I have unending respect for those who are just as, if not more, involved in their communities and jobs despite any seemingly unfair limitations imposed by nature or fate, what have you, than those in what I suppose I could call “average” circumstances. I have incorporated an NPC with a disability into our next game because of my desire to bring that respect and recognition to these scenarios. It should be normal and not at all a big deal to see a starring character with a disability, but until that day, representation has to start somewhere and I want to help in some way.
I think the key to avoiding offense is lots of solid research, coming from a supportive/humane POV, and also not making the diagnosis a focal point of the character. As in, they may live with a disability, but they aren’t fully represented by the disability, if that makes sense. I think there is merit in the fact that you have even considered it, are asking for feedback in order to approach it in a positive and constructive way, and I hope you can figure out a way to see your vision through! Good luck!