Neil's advice is good and covers most of your questions.
I'd just like to add a note to your question what you should ask in a survey. Personally, I wouldn't ask about prices and features if I were you -- at least, for face-to-face interviews.
Participants seldom know how much they would pay for something. They also tend to provide strategic answers: Their guesses are either too low (to influence your pricing decision) or too high (to raise the likeliness of seeing the product for real).
Most customers also seldom know what features they want or need. They also overestimate the amount of features and forget about the complexity it introduces.
In other words: Your clients want all possible features in a simple interface for the price of zero. (If you really want to go this route, research 'Conjoint analysis' as a survey method.)
Instead, I'd suggest you ask participants about their current work flow, any existing problems within that work flow, how much time they need for certain steps and how much it costs them to get these done.
If your application is already build, estimate how much time it takes a client to get it running and to keep it running.
Your advantages: First, you'll understand whether your prospects are aware about the problems you're trying to address. Second, you'll have detailed numbers on how much time your clients will save when using your application. Third, you'll have detailed numbers how much money they could save when using your application.
With these numbers you can easily calculate a price range for your application. They are also invaluable for any sales pitch you need to make in the future!
Nearly nothing beats the headline like: "Make US$ 26,145.34 more profit in just a few minutes..."
Hope that helps.