A few things in response:
What the design viewer says, goes. If it doesn't work there, it doesn't work. Similarly, what it displays is what the game reads, simple as that... though I only say this with 95% surity. Still pretty sure about that.
As for weight, the whole thing only weighs in a 1.5kg -- there's clips that weigh more than that, heh. Each point of minus on those mass modifers drops the weight by a half kg. The class 10 comp (which is what that class 15 defaults to and where the majority of the weight would come from for this thing) only weighs 10k, and you're fudging it down a full 12 kg. It's actually weightless, heh. Similarly, the battery's only one kg as is -- it would be the most efficient SF:0 power source in the game (barring further mods, of course) if yeh got it out of that thing.
Last bit, it looks like a comp bottoms out at 6 softwares installed, whatever their zeg costs happens to be. You could, however, just put in another computer component... and another, and another and another and... anyway, two comp 6s would fit your intended loadout just fine.
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As for the interface in general, it's always been a bit clunky for me, but I always assumed that was a limitation of the code more than anything else (check the old-ish item stacking thread, ferex). Easy way to re-size the ascii window to fit more info (without wrestling with my PoS OS, may Vista burn for all eternity), resort the pack, and a few other things would nice, heh, but GH's still got a fairly nice interface compared to some things out there, yanno'?
Anyway, hope at least some of this helps yeh out. If anyone notices something glaringly mistaken, correct me post haste, heh. It's been a bit since I monkied around with GH...