-Turrets are about on par with regular ships, but it depends on what type you're using. Basic turrets, as their name might suggest, are pretty weak. Flak and Missile turrets have pretty high damage, so they generay perform better if you've got a good economy going. And of course, mark level is a critical factor in strength. A Mk. I turret against, say a Mk V bomber is no contest.
-When placing turrets, remember to place them in range. Missile turrets I believe are the longest-range non-sniper turret. They're pretty cheap and if you place it so their range (the circle you see when placing one) is just encompassing the wormhole they can shoot most ships without being in range.
-Grav turrets can be under shields and still slow hostiles. This will greatly increase their time alive, giving your snipers and other long-range stuff to work away at the enemy. Again, mines placed in a line from the wormhole to command station will reduce a lot of threat, since the AI ships usually just make a beeline towards the command station.
-The AWS does tell you what wormhole to defend. It will appear red instead of the usual green after you build one. It only gives you this information on the planet it's built at, however.