Hello, I would like to work with you , I understand you want your sketch with a professional finish. You are right, if the sketches are already done do the job becomes easier.
I wonder what art style needs and for what age is your product , so you mentioned at the beginning I guess you want vector art , which I can do very well in illustrator .
Please visit my portfolio to get an idea of how I work.
If you want I can work in one of your pictures for you ensure the quality of my work.