Regarding the "emscripten-imposed file size problem", I've written a couple of alternative cross-platform headers which might help in this case (e.g. avoiding SDL). These enable WASM apps in the "dozens of KBytes" range, and you get native-platform support "for free":

https://github.com/floooh/sokol

Check out these samples and have a look at the size in the browser devtools which are IMHO quite sensible:

https://floooh.github.io/sokol-html5/

https://floooh.github.io/tiny8bit/

PS: really great writeup btw :)