To run a sample application that uses the BOS, you will need an Enterprise with BOS key. You cannot run this sample application with a DevForce Express key.
You don't need the BOS to access a network or remote database. You just need the right connection string. However, if you want secure and highly performant access to the database, you will need to be using the BOS.
If you want to use the BOS on a local area network, you don't have to use WCF or IIS. Look at the "Deployment" tutorial in the advanced tutorials.
If you want to allow your customers to have Internet access to your BOS, you will almost certainly want to use IIS or WCF.