Hello, I have experience in this segment, first I will make the sketches for approval, then after approval I start the first illustration with the color palette of the characters, then the illustration of the scenario.
I have been working as an illustrator for 30 years in the whole area of illustration, didactics and techniques, such as: sciences, biology, history, geography and infographics. It usually takes me from 2 days to a week to deliver my final project. I'll attach some services I've done for companies that are close to your subject. All the attached arts were created from clients' sketches. I am a creative professional and I like to be able to help with ideas to improve what you already have available.
Now if it's a project where you need someone in the long term, I'm also fully available, we've combined an amount of service or images per week or month, we set a weekly payment per milestone.
I need some more information to know your real need.
I am posting several jobs for companies like yours.
Thanks in advance.