Given the substantial initial investment and ongoing operational costs associated with establishing a poultry farm, encompassing land acquisition, infrastructure development, flock establishment, and ongoing feed and veterinary expenses, how can I develop a comprehensive business plan that accurately projects profitability over a five-year period, secures necessary funding from investors or lenders, and incorporates detailed contingency plans for unforeseen challenges such as disease outbreaks, market fluctuations, and economic downturns, ensuring the long-term viability and sustainability of my poultry farming enterprise?