Essar, did you ever play Battlefleet Gothic? The Tyranids had a table where the actions of their ships were generated from surrounding preconditions - a bit like a yes/ no chart. I've often thought that I could use that as a starting point for determining enemy ship behaviour. The rules are on t'interweb as PDFs, just requires some searching.
The main issue for me would be determining the random nature of the enemy's appearance and 2 Hour Wargames has a bunch of random generators that could help with that.