you can add 4 more weapons to each Frigate and Cruiser the main issue is that in large battles.... Effects Start De-spawning.
Its a shame that altho sins is an amazing modding platform in many ways its very limted
HasFighterMovement seems to line up to Movement speed and weapon cooldown, so you set your weapons to shoot a large volley as they do an attack run, otherwise the balance of alot of the ships will change. (eg keep there current dps by increasing damage but have them shoot every 14 seconds instead to line up with attack runs, ship speed and range effect this time.)
If you open up the mesh files in a text editor its a pretty simple matter to stick on new weapons, you can line them up on the Developer.exe or with a 3rd party program.
as for fire arcs You can have the same weapon point on the side of a ship shoot diagonally \ / they can then shoot right left and forwards.
The Advent Battleships side plasma weapons do this if you want something easy to copy, they will be the Weapon-1 with the highest X and lowest Z.