In my most recent game my first ship had a Laser (version 1) and the basic hull plating that you get from starship defenses. I put it on a Small hull and called it the "Flashlight". Heh.
That basic hull plating is pretty useless by itself, but my only intention when putting it on the ship was so I could take advantage of the defense assist modules on my military starbases. It worked, too. My I started my military bases with some missile defense assist and a couple beam weapon assists. Instantly my Flashlights were 3/0/0-0/3/0. The AI civ's ships were 0/2/0-0/0/0.
I ended up ignoring engines and life support on my warships throughout the entire game. I researched Warp Drive, but only for the intrinsic +1 speed bonus and +1 speed starbase module it provides. That left me more room for guns and defense. Also, everyone I fought was well within range of my ships. Sometimes they were at the limit, but that can be alleviated by the intrinsic range bonuses that life support tech provides.
Regarding defense systems, I found that they really helped. I pretty much always got the initiative, but I would rarely kill a ship outright after the first volley. The addition of one more gun wouldn't really have help, either, especially in the long run. Had I not used defenses, I would have been losing ships quite quickly, even if I won every battle. With defenses, the fights took longer, but I also took less damage and lost fewer ships.
Late in my last game, the Drengin took to putting a massive amount of defensive systems on their ships. I faced a bunch of battleships with a shield rating of 24 each and a mass damage rating of 12. Took forever to kill the things -- and those ships of mine were outfitted with shields and point defense. The reason why I could continue to win was because the Drengin went overboard on the defense, I always got the initiative, I had a massive tech advantage, and I had a maxed out military mine. Had he used some more balanced ships and reacted smarter to my approach, it certainly would not have been so easy, for me.