I think mimic interface is too far off. While there are prothestic limbs out there, they follow a very simple movement - tehre can be no talk of complexity here..
As far as direct control goes - the mecha might have a different weight distribution or inertia, but the pilot is the one who is charged of balancing it. Thus it would be in theory no different than fighting in a middle-aged armor. takes a while to get used to fighting in it, but after a while, it's like it isn't there.
Secondly, weapons integrated into the body could be fired by a special voice command or movement (like for instance, they way spiderman puts his hands when he fires his web). And come to think of it, who would need integrated weapons anyway? We're talking about a giant mecha. His normal machinegun would be at least like the A-10 Vulcan 30mm cannon, and than one can rip tanks in peaces.