As most of us are not 7 foot tall I would say that drywall leg extensions would be good for the feet as a prosthetic, but you would have to figure out an explanation for the gait. The hands as far as flexing there are options for that either with servos or wire control. And an explanation for the abnormal arm size, though a clever gauntlet setup could hide things nicely. Doable, but you would be hosed on slopes of any sort, let alone stairs.