Will this organization serve a niche that is already being served? If not,  

Do enough people care about it that funding is likely? If yes,  

What would the elevator speech be? This is a one minute explanation of the organization, its purpose, activities, and its stakeholders. This will be important for enlisting support of funders, volunteers, and staff. If the speech comes easily to mind then,

What funding sources are possible? If there are enough then,

What other organizations are already providing a similar service? How would this organization be different? If the answer is obvious, then perhaps it is time to proceed.