In terms of the drawing aspects, working on SVG or raw canvas drawing each have some drawbacks. If you don't need to output vector files, I recommend PixiJS, which gives you a stage-based display chain on top of WebGL where you can mix free-form line drawing with pre-made sprites. I used to write a ton of procedural graphics with Actionscript, and this has been my clearest path to continue on those projects. Some AS3 drawing code is almost directly portable.

https://www.pixijs.com/