Will a Mac Mini server suit my needs?

We are a small business and run mostly windows applications related to the production agriculture we do. We have however equipped the employees with iPhones and use iPad's regularily for record keeping in equipment and around the shop.

We use gmail, were running google apps until the change in fee structure, and currently keep files on external drives connected to a pogoplug device.

We are moving offices and I am taking this as an opportunity to upgrade the system.

We are also in the process of using FileMaker Pro to build a customized database solution for the business. This solution will not replace the need for windows applications in the near to mid term.

I have zero interest in hosting email, but could see hosting a website in the future.

Would like to be able to keep all files on the server and be able to access them from anywhere over the Internet.

Should I buy a Mac mini with server installed or pay for hosting?