Considering the bulk of that "brick"-thing, you need strong legs that look like they can carry the weight. So #1 is out, รค3 looks clunky as hell. i'd go for #2.
As said, the legs need to be strong enough to support the massive weight of the thing. The arms in general look too spindly for this thing. Increase shoulders and arms. This helps with your third bullet too.
Depends on your chosen faction. Cables, rivets, plating, symbols...
But mostly, if you want feedback, you need to improve your design with more details. Because, honstely, this is. a tad underwhelming