Espruino on ESP8266

I have windows

I'd seriously suggest you use a VM and build under Linux (you could probably still do this while using eclipse on Windows if you wanted). The Espruino build has to run some Python scripts to create things like hard-coded symbol tables, so I imagine you'll be making life a lot harder for yourself.

How big is the compiled Espruino program? Will it fit in 512K of Flash?

It depends what's included... it should compile down to about 100kB of ARM thumb with -Os if there's no networking or USB in there - but I have no idea how compact the xtensa instruction set is.

However unless you build with RELEASE=1 make it'll include a bunch of assertions which really bulk the binary size up (although not that much!).

I think everything is being flagged as to be loaded from RAM and that of course won't fit

I imagine he's probably just tweaked the linker script so this doesn't happen?

If you tried compiling under Linux with a VM it might 'just work'.