Seeking advice on the feasibility of a project concept

Hi all,

Thank you again for your suggestions, they've been very helpful :)

I probably ought to have mentioned this before, but this is my first real foray into electrical engineering (primary focus is as a web developer), so this is still all very shiny, new (and a little petrifying!) to me.

@Gordon, your suggestion of Ciseco modules (particularly ERF/Slice of Radio) sounds really appealing. If I might trouble you for some help, I've a couple of queries;

1. Whilst I've reviewed the site's information on MOSFETs, I'm afraid
   that I don't know how I could use them in relation to the Espruino's
   internal clock for switching serial on and off. Do you know of any
   resources you could particularly recommend for this?
   
2. The chip antenna is certainly respectable for range, it does seem to
   suggest that a wire whip antenna could get that 500m range (300m for
   Slice of Radio). However, I've been going completely spare trying to
   find anywhere that sells simple 82.2mm wire whip antenna that will
   interface with the board - do you or anyone else know where these
   can be purchased from, or am I missing a trick?
   
   

My apologies if I do seem a little slow on the uptake on this, and again, everyone's help has been nothing short of amazing :)