Is it Realistic to Write a Quadraplegic Character That Studies Art?
The reason you’re having so much trouble finding solid info is because CP is a really broad diagnosis.
One person with CP has a mild limp.
Another person with CP has full use of their legs but a weak and atrophied hand they keep pressed against their chest.
Yet another CP can’t use any of their limbs and can barely turn their head.
All of these people have have CP, but the symptoms are wildly different.
So for your character, the fine motor skills they have is whatever fine motors skills you happen to describe them having.
Is it realistic for someone with dexterity issues to study illustration and want to be an illustrator? Of course is it.
There are some fucking wonderful illustrators who happen to be quadriplegics. They’re really good at what they do. Full stop. You should seek them out and ask them what cool shit they’ve come up with in order to create the awesome art they do with tools originally designed for folks with two working hands.