Question about setDeepSleep

if a GPIO pin is on output and high, and I place a drain of 10mA - LED to GND with current limiting resistor - does that mean that the 'processor' draws something between 10.5..11mA - 10 for the LED and some 0.5+mA for the rest of the chip?

Yes, that's right.

I'm not sure what you mean about the circular buffer? I had hoped to expose the 'event queue' (also a circular buffer) at some point. It'd mean that native functions could then do processing of things like radio signals and could poke data straight into that queue for handing by JS in the main event loop.

If you're willing to recompile Espruino with your own changes then you can do that kind of thing pretty easily at the moment, but the trick would be exposing it to code that was uploaded by the Web IDE.