When you have to communicate decisions to stakeholders, one possibility is to use a requirements document. Unfortunately, requirements documents are seldom read promptly, and you risk that your project will run out of steam before stakeholders get back to you.
Another strategy is to use something different in order to avoid the risk of "taking a couple of days to get everyone on the same page": the task analysis grid is an interesting alternative to the standard requirements documents.
- Map the steps required to successfully undertake the task.
- Indicate the resources required to complete each step. Include human resources, stationery, equipment, and costs.
- Indicate the time taken to accomplish each step.
- Highlight any areas where you believe errors could occur or any areas where you receive contradicting information regarding how a step is completed.
The goal is to see the scope of the project and the whole features of the first and future releases on the same page in a unique schematic description.