We're working on achievements, yes. We already have cloud saving going with the web-player version, but we can probably make Steam save your local progress to the Steamcloud. You just wouldn't be able to play the same Kingdom on the web-player or mobile version if you didn't also sync that with our system too
Don't worry, we'll have all of those sorts of issues worked out before release. Suffice to say, we'll try to use what Steam offers us as much as possible.