Weapons are linear. Most keep to 5 damage per second, per block. So if the block has a reload of 10 seconds, it gains 50 damage for every block you place. Power cost is linear as well, 10 point of power for every point of damage (so you need 50 regen per weapon block). I believe the only exception to this is missile+Pulse, which has reduced damage for balance reasons, and Beams, which has a few bugs with power costs last I heard.
Stats like Range and projectile speed are fixed in relation to server sector size and server speed respectively. When you add a slave, it changes those values in a linear manner as.
If Cannons have a range of 5km and Cannons+beam have a range of 10km, then Cannons+50%Beam would have a range of 7.5km (an example)
Effects attached to weapons increase the weapon group (so add the 5 dps/block as well) and then apply their effects. When not attached to a weapon, they give a boost depending on the % of the ship's block count they take up. Ion will give 60% resistance (maximum) when it is 10% of the ship's mass. If it takes up 5% of the mass, you gain 30% resistance.
My explanation was probably bad, but weapons and effects are pretty much linear in every respect.