In my personal use of Imperial Navy, I like to either have lots of novas and a more long range fleet or use no novas and get in there quickly. The problem I have with going a line formation with your current line-up is that your Lunars will want to get close and torpedo shotgun them and the Mars cruisers will want to hang back and nova and provide ordinance. You will have to break them up at some point. Where your Lunars will want to all ahead full to get close, your Mars cruisers will be reloading and hanging back.
Personally, I would drop Mars cruisers for Dictators which will be able to stick to the torpedo line formation and provide ordinance support. Also, I am a fan of Armageddons and Overlords. I would consider those as well if you have the points.
Here is what I would chose...
Armageddon + Tyrant w/ range upgrade (these would be in the middle of the line of the 6 or maybe furthest away from there you think the enemy ships are heading)
2 Lunars (these would be coupled on the side of the line where you think the enemy fleet is going)
2 Dictators (these would either be coupled on the line furthest from where you think the enemy fleet is going or in the middle)
Hope that helps!