Other than the Disposable unit requiring many many calories to upkeep and also be infront, I have no idea how that thing is gonna properly shoulder a rifle like that, and being a quadruped, can’t compensate any horizontal tracking like a biped would.  
Also the lack of access for reloading what seems to be highly inaccurate dual artillery cannons makes it quickly dead weight but excessive dead weight. Those Breach Blocks are heavy as hell and I doubt the short barrels could ever allow for proper expansion to propel any ordinance other than rocket assisted ordinance 13 Kilometers let alone a mere 3.
 
Recess the Organic unit behind armor into the interior and have the arms be more forward ahead of any obstructions like sensors or structural supports, re-evaluate if you want dual Artillery ready and portable or just be portable on a modular flat bed construction for more versatility.
 
Also, re-evaluate the value in having a happy and experienced pilot. Any Operator would understand experience allows what ever you employ on the field to be 100% used and no features wasted. Like a top “Chainsaw handle” for your LMG on a quadruped that can’t hip fire past a certain maybe 5 degrees horizontally.  
Lowering the shoulders to allow more effective hulldown/cover fighting  
Making the front legs bend outward to allow crouching? When it sits I have no doubt the knees will meet half way.  
Re-evaluate wanting actual arms on this model, they are too long to allow accurate and quick reaction firing due to the distance they have away from their shoulder joint and how lanky they are.