Just for your info, there is a small bug with the brush when you increase its size and then decrease again.
Anyway, congrats for the project! :)
Re: the bug - what kind of issue are you seeing when you change brush size? I haven't noticed anything myself, but I'm also not sure what to look for.
Hey, I'm sorry if I was too vague.
What I see is that the brush starts to draw "dirty" lines with some pixels on the side, instead drawing single pixels. Like if it was not reset to the original configuration.
Here are the steps to reproduce:
1. open a new document and zoom in
2. draw a curve with minimum brush size (1)
3. increase brush size to the maximum (20)
4. draw another curve
5. decrease brush size to the minimum (1)
6. draw another curve
In my case I see that the line of step 6 is different from step 2. Here is a screen shot of the three curves: