Terror ships are pretty much a must-have, but other than that you have lots of options (and I've heard that one like taking just a hulk and swarms of escorts, so even that rule is flexible).
Kill kruisers have always disappointed me and feel overpriced for what they bring.
I've had lots of hilarity but not much success running brute ramships (except that one game that I hit a chaos cruiser with a full skwadron of 8 due to perfect positioning and did something like 22 hits before brace saves). My favorite escorts are the ones with 'eavy guns (don't remember the name), but they're pretty limited by range and maneuverability, so you want some more options in your fleet (I like pairing them with torpedo escorts to trry to herd opponents towards them)