Writing modular code using "require"

For reliable timing, you'll need a crystal (32.768khz) to solder onto the board (see http://www.espruino.com/Clocks ) or (probably better, if you're controlling your heat with it ;-) ) an external RTC module (with a battery, so even when the espruino resets, it'll keep time) - there's already a module for the DS3231, used in the most common RTC boards.

Espruino runs normal javascript - but you have to be much more aware of memory usage, since it's running on a microcontroller with 48k of ram, some of that used for the interpreter and stack. The length of the code actually becomes relevant.