Alfraks Putting nothing but armor/shields in the nose of a broadsider gives you some more flexibility, the nose is going to take a lot of hits as you spin and you can use it to block all fire from one ship while shooting at others or stalling or reloading or whatever. That one's nose crumbles before the sides do.
Shield-less ships with only cannons and missiles can work with surprisingly few reactors, you could cut the number of reactors in half and still have more energy than you need (but a lot more money).