Hi, thewaver, and welcome to the forums!
Placement does affect range slightly (or more than slightly if you’re using a particularly large hull). A weapon’s range (minimum and maximum) are measured from the position of the slot you drop it into on the design screen. Do note that an enemy ship isn’t considered in range until the center of that ship is within a weapon’s maximum range.
The multiple hardpoints are strictly a graphical element; you don’t get extra weapons or anything silly like that. If you place a beam weapon into a multi-turret, a beam will fire from each turret, connecting at the target (except for the Swarm Disruptor, which converges like the Death Star). For missiles, bullets and plasma, you will still only get one weapon discharge each time the weapon fires.