So first thing first, completely forget strength with this guy so praise the lord no more use of gazillion formas so that we can fit umbra mods. His ability damage is too low and wrong type of damage type to be worth building for and strength doesn't affect anything else -- well other than his 2nd ability because the 100% damage reduction decreases if your strength is below 100%. And surprisingly, the buff you receive increases with duration instead of strength, so, awesome! It's lot easier to build for duration than strength. So for Gauss, here what I think you should prioritize from most to least: Duration, Energy Pool/Efficiency, and then Range.
And here's why:
You need to keep spamming his first ability to keep his battery fully charged as long as possible so obviously you need large amount of energy.
And obviously having large duration will allow you to keep his 2nd ability's shield up as long as possible for that 100% damage reduction as long as you keep the battery capped.
His third is pretty interesting, combine with high duration and fair range you can freeze any enemies that got caught for more than 20 sec! That's pretty cool. I'd prefer freeze over fire, because one, it completely immobilize enemies, and two, it fills up your battery depending on the number of enemies. The blast proc doesn't have status durations and it's not the best elemental damage either so I won't bother.
Now for his 4th with maxed duration.... Here's a picture:
That god damn 230% fire rate increase. Reload speed and attack speed is also awesome. Holster speed is nice if your place style involves switching weapons alot.
So yeah if you are building for Gauss prioritize duration, energy, and then range. And sadly I wouldn't recommend using overextended like I mentioned above with strength.
So what are you guys' thoughts about him?