This obviously depends highly on the domain/industry that you are in.

I can create a market place for, say, legal advice, tomorrow and have plenty of demand. I just need to make it a market place for free legal advice from top-lawyers. However, the supply will be hard to come by. Or I could get plenty of supply if I make it a marketplace for $1000/hr legal advice, no education required for the supplier. In which case the demand will be lacking. It can be quite tricky to find the equlibrium (indeed one might not exist) and I don't see how any generic advice could help. If you have managed this though, your problem should only be about reaching people. In that case, you either need to find the "home turf" of your suppliers or your buyers depending on which party you lack, go there and announce that people are looking to pay them money or people will help them solve their problem.

I guess this depends a lot on what sort of questions you are talking about. If it's life and love and "soft" things like that, intuition is probably better than any decision based on "data", what ever that would be. On the other hand, if you just have an intuition that you should set the price at $1,000 rather than $99, it might be worth at least exploring your own thinking.
There is nothing wrong with having strong intuition and then looking for data to back it up with. It's a sound psychological foundation -- read Antonio Damasio's book Descartes' Error for a fascinating exploration of this idea. However, intuition can be wrong. "Following your gut" is sometimes praised as if gut feelings are some super natural source of knowledge. They are not. They should be guidelines, but you should still question them and be open to new realizations. Besides from conversations with people of different views, 5 whys (http://en.wikipedia.org/wiki/5_Whys) might be a useful tool for this.

If I was just starting out, I'd consider learning Meteor (https://www.meteor.com/). It's just entered version 1.0 and after working with it for a little less than a year I do have some issues with it but it still makes for a very solid framework that gets you up and running very fast. You would only need to learn Javascript, and you can slowly work your way towards nodejs from there (which Meteor is based on) if you want to, or you could get the basics down and focus on learning design if you prefer.

I'd add one thing to the other good answers here.
I think this is becoming less frequent as startups are becoming cool and thereby respected, but I still see some entrepreneurs "playing company". They print business cards, design logos and come up with slogans. Maybe they even talk with investors. All the stuff that startups do, except for the important thing: customer and product development.