I would like to create both of the following:
A graphic novel. I would like to be able to sketch, draw and preferably color all the panels myself.
A textbook in mathematics for children ages 6-16. I would like to be able to create nice illustrations of characters, or items like coins, bottles, footballs etc. to be displayed throughout the book. Preferably, I would also be able to design some nice geometric figures for the geometry chapters.
I am a complete novice, and I do not know where to start. I have no experience using any tools except I have played around with the TikZ Package in LaTeX and also the drawing app Leonardo. I do own a Windows Surface Pro. Any recommended tools should preferably have a one-time cost, although it is not a necessity. I need to be able to self learn how to use the tool, that is, I should be able to read a book or watch a video series to learn. In principle, I do not have a time limit, although it would be nice to be able to produce results within a 5-year scope, working on a hobby basis.
By "tool" I mean some kind of software or tablet. Keep in mind that I am a complete novice and I might not know what I actually want.
Which tools should I learn how to use when I have the combined goal of creating a graphic novel and a math textbook?