I'm going to lead a creative workshop for a tech company that want to make a new product that resembles an app-store. The goal of the workshop is to come up with concepts, sketches and mockups for a software in which a user can browse assets and upload them to an external device. We will be 6-7 people with different background and experiences (graphical designer, marketing, product owner, expert user, programmer). No one have previous experience with sketching graphical user interfaces.
The software platform will most likely be a responsive web site to accommodate desktop computers as well as mobile phones and tablets. Because of this, my first idea was to take a 'mobile first' approach on the workshop where the participants will be limited to sketching ideas for a mobile app. This could in theory lead to designs with a stronger focus on core functionality. On the other hand it can turn out to be too limiting. As we all know; a simple design is often very hard work, and for a novice it's perhaps easier to express your idéas without limitations.
What are the recommendations for a situation like this? Is it wise to take a 'mobile first' approach for a creative workshop with participants that are inexperienced with sketching?