Combat works the same for NPCs and for PCs where skills/armour/weapons are concerned, so just think of them each as a squishier you that can die.
Ideally you'll want NPCs with high dexterity so they can hit (and weapon skill for a little more hit if they are still missing), dodge so they can avoid getting hit, and strength for HP.
If you are certain you can keep them out of enemy range you don't need to worry much about dodge/strength right away and can just dump the points into their ability to hit. Armour won't matter either if you're paying attention to enemy range, but if your goal is to keep them out of the line of fire altogether, you're better off targeting creature squads since they have more consistent ranges, whereas bandits tend to cover a broad spread.
As to race, anything that has good skills and race multiplier. Hutts, Noghri, Abyssins, and Togorians are popular choices, but there are many races with some good skills and decent RM so you have a wide selection.