Audio: I've never messed with it but I believe it works.
Compact database: I know this used to work when I last used it a couple of years ago, but it's possible it has become broken since then. One thing with it, ensure that you have a game saved in the database before trying to compact it, you will corrupt it if you do not.
Lasers will have much, much longer listed maximum ranges than your beam firecontrols can supply. This is intentional. Steve made a deliberate design decision to not track packets of beam weapon fire from one increment to the next. Your beam firecontrol, when the range tech has been fully researched, caps out at the distance light can travel in a 5 second increment.
However, longer range lasers still benefit you. This is due to the fact that lasers, like many other beam weapons, suffer damage falloff with range. So a longer ranged laser means that when you hit the limit imposed by the firecontrol less of the maximum damage has been lost.
To understand turrets you first need to understand tracking speed. Tracking speed is used to determine the chance to hit a moving target, in particular, if the target is moving faster than your tracking speed you suffer a penalty to hit. There are actually two types, the tracking speed of your beam firecontrol, and the tracking speed of your weapon. The one of these that is lowest is used when determining your chance to hit.
Your firecontrol tracking speed is simply your base tracking speed determined by your level of research multiplied by the modifier you used when designing the firecontrol.
Your weapon tracking speed is the highest of the speed of the ship it is mounted on or the base tracking speed. Where turrets come in is that, you can design them to have a specific tracking speed which replaces the speed of the ship when determining the weapon tracking speed above. This however comes at a certain cost in additional size compared to an unturreted weapon, based upon the turret tracking speed techline.
The primary time you will want to use turrets is when you are attempting to engage targets that are much faster than your ship such as fighters or higher tech NPR's or for point defence against missiles.