Is Espruino right for my project?

could you imagine the Espruino graphics have the same api as the 2D context of an html canvas?

For drawing text, yes - for lines etc, it's possible but not without a lot of overhead (as the HTML5 Canvas lets you define a path, and then 'stroke' or 'fill' it afterwards).

It'd be a lot easier to do as you say, but the other way around: Create an Espruino-style graphics object but on the PC (where you have enough resources for the adaptor).