With the help of a kind forum user I've now got the line of sight and pathseeking mechanism we need working beautifully. Thank you!
In essence it's a single enemy patrolling around until it sees you, then it gives chase until you either kill it or hide from it. If it can no longer see you, it looks around for a bit and then goes back home.
What i'd like to happen is that similar sprites nearby, that may not have seen you to take notice of the alerted sprite and move to the hunting mode automatically?