If an initial assessment results in the decision to move to a more detailed feasibility, agreement will be needed on the further work that will be required and how to secure the resources necessary to make it happen.
The information gathered for the initial assessment will have to be researched in more detail and verified with the benefit of professional advice. This will provide important information to be included in the project business plan.
A Feasibility Study report can help your group to seek support, but it is also possible to simply include results of the detailed feasibility process for the project into the business plan.
Either way the feasibility study or business plan should draw on research or other evidence which supports assumptions made about the projected capital and revenue income proposals to manage the project when it is complete.