It doesn't strike me as making sense that a 20-foot mech, where the pilot is completely encased in the torso, should enhance the pilot's strength for sword swings....
I'd be more inclined to treat it as a form of golem that the pilot controls, with it's own AC, Strength, Dexterity, Hit Points, senses, and the like, but using the pilot's Intelligence, Wisdom, Charisma, BAB, and the like (for most things).
Also, I'd give it BlindSense (or perhaps BlindSight) over See Invisiblity; the Sonar lets you know something's there that isn't picked up on the camera, but not what, and the resolution is much, much lower (also - how the heck does a camera pick up something on the Etherial Plane?).
Basically, stat out a golem, remove what doesn't make sense (e.g., Magic Immunity, immunity to charms, phantasms, and the like; BAB, Int, Wis, and Charisma) and replace those with the pilot's abilities (so the Fighter is much better at hitting things with a mech than is the Cleric). Mind you, it also requires a skill check (Mech Pilot(Int)(Trained Only)) in order to work properly (similar to controlling an untrained mount in combat, but different DC's for different functions); so while the Wizard can get it to do what he wants more often (use Darkvision, low-light vision, climb a ladder...), the Fighter hits more accurately when he finally does get it to do what he wants (break things).
Also, possibly give it ranks in certain skills (based on an ability score of -) that replace the pilot's (e.g., Listen: that sound amplification makes it fairly easy to hear that mis-step, but just gets in the way of someone who already could, and the definition is lost for the step that wasn't mis-placed on the other side of the room; Spot: sure, the threat-highlighting software running on a screen at 10,000 pixels per inch that's 30x30 inches is great for letting you know that the mouse behind you isn't a threat, but that the big metal blob on the other side of the curtain is... but if you already knew about the mouse, and could read the serial numbers on the other mech with your own eyes despite the curtain, then the screen's highlighting just distracts you from noticing the teltale sign of that land-mine you are about to step on.....) Sure, at those tech-levels, they will probably be decent aids.... but I'd want the 20th level sword-wielding Fighter to cut it to ribbons, the Rouge-20 to sneak past it (and maybe find a chink in the armor and cut a fuel line (Sneak Attack!)), the Cleric-20 to turn it against it's masters with Animate Object (wouldn't that just be cool... well, when not in the pilot's seat....) and the Wizard-20 to blast it into oblivion.