I have completed that level, and it is pretty hard :) i suggest for the space combat keep energy to shields until the majority have a gap/weakness in their shields. auto rifles are good :D you made a very good choice for ground combat as they do lots of damage and do short bursts, as well as fully automatic for 3 secs.
Pistols are used for short ranged, but there are 2 types of phaser pistol. The stun pistol shoots a concentrated beam at the target, as well as stunning as secondary fire. The wide beam pistol acts as a handheld shotgun, it targets several enemies in one shot. Rifles have several types, there is the pulsewave (as said…