The second is the local bind address. Often, something like "0.0.0.0" is fine, but if your host is multihomed you may want to be more specific. I recommend you don't set one unless you know why you might have to.Typically you won't create your own remote devices. These are created automatically when you receive IAm messages (in response to your WhoIs).The instance number is an identifier that typically won't change, and so can in many cases be used to uniquely identify a piece of equipment. It is also what is referenced in a WhoIs request when you specify limits.
Network is only required when - like you - the BACnet installation consists of more than one network. The network number is then an identifier of the network segment on which the device lives.