Very nice ! I've played a little with Paint and other than included shapes all of the lines are done freehand , not an easy thing to do . Again you've obviously had a lot of practice . I've been using Paint.net for many years now for most of my stuff and I have Corel Draw when I need to do artwork for decals .
Paint.net is FREE and is like MS Paint on Steroids ! You might try it , once you get used to the features it's amazing what can be done with it . They also have a forum for help and to add all kinds of fancy stuff to it . Below is a link .
https://www.getpaint.net/index.html