Using sticky notes as bookmarks could be good way to keep track of your projects in your notebook, or even numbering each page as you get to it, then keeping a table of contents on the first page.
I never bring my notebook with me outside of my house (besides to my friend's places sometimes).
Sticking with MsPaint is totally fine, but it can just be difficult to work with.
I'm far too used to being able to switch layers!
GhostPepperNG
I'd really recommend getting a little notebook to regularly sketch in!
I've had multiple for a few years now and even just sketching things while watching youtube has been super great.
I think digital art can be a pain to set up everytime, so it's cool to just be able to sketch whatever, whenever.
I would also recommend Kirta!
It's the art software I use, and it's great for both drawing and animating.
HeroPapaya
I'm in a special state right now. Sorry about this hefty reply.
A little notebook for sketches would be a neat thing to have. I could see myself getting it out time to time; on the bus, in the park, at some random restaurant etc. The problem would be that I absolutely want to hide my art from the public eye, especially in the phase of creating it (not a problem if used at home of course). Also, you made me think of sketching references irl for use in digital art. That could be convenient and fun.
This is not directly related but I think I'd need another notebook as a journal, and one for random ideas as well. The best system for me so far when it comes to maintaining a resemblance of structure has been just having empty pages lying around and if I get a random idea I can write it down and later assign it to a new or existing (real life) folder. That way is much more streamlined than having multiple ideas in a single notebook, which are then mixed up with other ideas and hard to find, or forgotten etc.. artworks can be seen as "projects". I need to get better at labelling the folders.
I'm really bad at planning things, and if I do plan stuff it's likely that I won't even follow my planning, since I get sidetracked too much; for better or worse since those side tracks can be valuable.
As for leaving ms paint behind, I don't think I will. Part of why I use it is because it's frowned upon, it's like I want to prove something to myself. Why use a chainsaw if you can just use a saw?☺
However in this big box of jumbled thoughts there are (of course) plans and ideas for animations. I often play with (and absolutely dread, with some kind of morbid curiosity,) the thought of animating a frame by frame animation with ms paint. Given that creating an image in paint might take me somewhere around 4 - 8 hours the extreme amount of effort it would take to animate is curious to think about.
Krita could be an alternative, I probably wouldn't live long enough to create an animation with paint and it's unlikely that I would pull through if I actually tried doing it. I've looked some at the tips given by newgrounds too: https://www.newgrounds.com/wiki/creator-resources/animation-resources