A revenue stream is the strategy used by a company to generate cash from each customer segments - so if you have multiple customer segments, you may have multiple revenue streams.

A Pricing Model is the tactics you'll use to set the price in each of your customer segments. To determine the pricing, you need to understand the value they are willing to pay for. When you're first making your assumptions, you can guess what the pricing could be, but you'll quickly validate how much they are currently paying (and for what value), and how they are currently paying.