1. What is your goal? What do you want your players to get out of it? What is your project goal? How does it relate to your game goal?
2. Where are you going to play this? In the galleries, or out? Both? Why did you choose that space? What does the game play have to do with that space?
3. How much can you spend? Think money and time. Do you have the staff to make the game? Play the game? Maintain the same?
4. Who is playing this game? Who is your audience? What do they like to do? How do you know? What are their limitations? What are their strengths?
Also, each answer effects the answers to each of the other questions. In other words, think wholistically. As you answer each question, reflect on your ideas.
After thinking about those big issues, you then need to expect to take lots of time developing, testing, and iterating. A seamless game often has hours and hours of prep time to get to that perfect game play.
For my other posts on games: