The number of samples required to have a successful model depends on the complexity of the problem you are trying to solve. For simple cases, sugar and water solutions at a single temperature for example, a few samples might be enough. For more complex models like the ones Consumer Physics makes for the SCiO App, hundreds of samples scanned in multiple temperatures and conditions are required.
It is best practice to iterate between the data collection and model creation phases until the desired performance is achieved.
(Relevant Product: SCiO DevKit)