Most businesses use the same sorts of information on invoices: contact information, sequential invoice numbers, etc. Because of the unique nature of freelance work compared to other businesses, especially for freelance invoices, it should be adapted to reflect these differences.
A job invoice is intended to provide an estimate to clients for how much a project will cost based on parts, labor, and other expenses. A job invoice is not the same as an official quote or contract. If you are a construction contractor or other service provider, you may need to offer clients an initial estimate to give them an idea of the scope of the project. While this is not an official quote, it is good to be realistic about potential costs so that clients understand what they are getting into. Consider providing more than one estimate - one based on the likely cost and another that includes costs for complications that could arise.