Start now.
Building a product and marketing it are two completely different things. Most of your concerns are connected to the marketing aspect (no connections etc) but there doesn't seem to be anything stopping your from building it?
If you build this thing and it is a flop then you still come out with a few wins: you show yourself to be someone capable of building a complete/ussable system and you have something to put onto your CV. You'll also probably learn a bunch of new things and come out a better developer.
Once you've built a proof of concept/MVP then you are in a better position to attract some people: showing your work to people is going to get more interest than "I've got this idea but I've done nothing with it" will.
Sales and marketing are a whole different ballgame and are fricking hard but I don't think you need to worry about those yet. Build the thing first, then worry. You have nothing to lose from building it and everything to gain.
"Would you focus on networking and save your ideas until you felt like you were part of the world? Would you focus on saving money, and plan to move and get a foothold in California? Would you ask for time off work and develop a prototype in private?"
None of those, I would build the prototype in my spare time, the safest option as you still have your status quo if the product does not take off. The Web gives us freedom to start companies for next to no money from anywhere in the world, the fact you are not in Silicon Valley does not hold you back at all.
Stop looking for excuses and getting to work!
Good luck.