Q. Power and storage consumption

The F401 chip in the Pico also has much better clock control - the CPU can slow itself down from 84Mhz, saving a lot of power. That's something I plan on adding soon too

How slower can it be clocked? ...down to static? (like some CMOS uCs that were/are sent to space? ...down to single steppinh the clock? (Of course, that would disable wake ups, etc.).

It is for sure an interesting feature...

missing the first byte or so You can do setWatch on the serial signal, but by the time the Pico has woken up you'll have missed the first character or so of the data

How fast is the thing moving that you track? ...and what is the resolution you expect? This may together with sending GPS to standby/sleep may give you various types of relieves:

1. larger intervals than 2 seconds
   
2. if delta from last position is less than your resolution (and of course the gps resolution), you drop / do not keep the tracking point
   
3. not the gps is the clocking thing but Espruino. In other words Espruino timer wakes Espruino up, wakes up GPS and goes to sleep for the time GPS is waking up, comes out of sleep and is ready when GPS is sending data. Some GPS can send data 10 lines / s, so Espruino does not need to hangout awake too long in case it misses, it just has to stay up until it gets a complete set of data. Afer that it puts GPS to 'sleep', and goes to sleep itself as well.