Some additional thoughts. (I settled with PA turrets getting +1 to hit and causing 2 hits plus a radiation hit.)
Plasma and fusion guns will be useless at ranges of over 1 hex. I have seen data that suggests a modern plasma weapon would fire a plasma bolt at around 100km/s, even assuming an order of magnitude increase due to TL that is still only 1000km/s - it takes 10 seconds for the plasma bolt to hit something 10,000km away.
As a pulsed weapon it would get the pulse laser -1DM to hit, and I would also grant the 2 damage, 3 for a fusion gun.
Rapid pulse plasma and fusion weapons would make for excellent anti-missile point defence so a bonus for anti-missile fire would be in order.