It's not unusual for flat panels on large aircraft to appear rippled when the aircraft is at rest. There's a considerable amount of flexibility built into them, and the skin will give it away in some configurations. It's a characteristic that's a bit more obvious on Boeing products than most others. The B52 has been completely reskinned at least once, and has had several partial reskinning programmes.
The normal G envelope for large aircraft is -1 to +2.5g, and is stipulated for passenger aircraft by international regulation. This accommodates the likely worst that severe turbulence will incur, rather than any ambitious manoeuvre capability. I'd be surprised if the B52 is significantly different from that. The extremely manoeuvrable C130 that I used to fly years ago has a slightly wider G envelope than that, but not much.
The B52's weird undercarriage configuration was a hangover from the B47 design from which it was derived. The high-set and very thin wing mitigated against conventional wing-mounted gear. The flexibility of the wing and its large size (for the time) meant that there was rather less scope for the 'wing-down' crosswind technique than was ideal, and so they hit on the idea of castoring all of the four main gear legs to allow a flat, drift-offset landing technique. The B737 has a similar castoring capability because of its very low-set engines, though the main gear isn't steerable.
