If your customer base is really that broad, then start talking to random people. It won't be long until you find a potential customer. Make your product work for that customer.
Also you should read http://www.paulgraham.com/startupideas.html. Pay close attention to the section labeled "Well". Odds are that, no matter how much you like your idea, you've chosen a poor idea to make a startup out of. Try to find a more focused variant to start with.
It certainly would be much 'easier' to have a niche to target.
I spent a year work on a product based on some informal surveys and a lot of assumption. Luckily it doesn't cost me a lot to run it, so I can keep it going and continue plucking away, but while it was a good learning tool, I also learned that trying to find a niche would be much nicer to start with.
Also you should read http://www.paulgraham.com/startupideas.html. Pay close attention to the section labeled "Well". Odds are that, no matter how much you like your idea, you've chosen a poor idea to make a startup out of. Try to find a more focused variant to start with.