Hello,
I have seen your requirement and I am glad to tell you that i have already created two drawing apps in past.
In short, I have already implemented features of freehand drawing on canvas, coloring , erasing, saving to sd card and sahring, inttegrating admobs
I can share you the screenshots and you will find how it matches to your requirements.
Please discuss further with me as I am a prefect candidate for this project.
We will finalise the time and cost after a small discussion with you.
Overall,
I am 4yrs experienced in android development and already created more than 10apps.4 of my apps are still live on store.