Is Espruino right for my project?

I'm afraid I don't have time to read through all of this right now - but in short:

• You don't need to mess around with canvasses, you just need to create a special 'arraybuffer' graphics - see here
  
• I'd really advise against writing all your own graphics library (unless it's done just to make the PC look like Espruino). Espruino graphics is quite fast because it's done in native C code internally, but as soon as you start writing to pixels by hand in Espruino you'll find that everything runs too slowly.