Hey, sure thing, glad to hear you are interested in trying it out!
So to start, there's no particular order on how to do stuff with compose web yet, but I started drafting some things around to create something resembling an API.
Right now, I created a couple of wrappers around document.createElement with "tag" function, you can see examples of how to use it on "h1" or "br". You can start by writing a similar "canvas" function and work from there.
As for unstable compiler version, depends on which compiler you mean. Changes to compose compiler are not yet merged, so you have to use setup from my repo for now. As for Kotlin compiler, it is compatible with 1.4.21, i think, so you should be fine here :)