Execute.

Is there a critical mass of value that someone will care about the problem you are solving for them?

The size of the problem you are solving and well you solve it generates the value. That then dictates what (if anything) you can charge. The number of people who have that problem defines your market size. That might give you an indication of the type of business/startup you have - is it a high growth startup, or in the case of a problem being solved where the market is not very large, maybe it's a life style business. Pete Thiels excellent book from last year talks about this and is certainly worth a read http://ajs.io/bookzerotoone.

Wikipedia says: A business model describes the rationale of how an organisation creates, delivers and captures value.

Or in my words: your business model is the way you profit from the value you create for others.

The good news is, starting simple has lots of benefits to usability, UI, message to market and capturing your first 100, 100, 10,000 users or customers. Go-to-market is where many startups fail most, not the technology, so that is something you should focus on and simplicity -provided your idea is part of a bigger vision- is a great place to start.