Update - I got the Boxster put back together with "new used" substitute crankshaft pulley, 3 new bearings pressed into the idler and tensioner pulleys, and with things cleaned up in the area. It was getting dark and late so I didn't get any videos afterwards, but the outer and inner faces of the new pulley still wobble to some degree, bit at least now the ribbed surfaces that guide the belt appear to be perfectly straight and true, so it's definitely an improvement!
There was no damaged keyway on the old pulley, like I was suspecting. It was either just manufactured poorly, or got bent (perhaps by a careless previous mechanic) somewhere along the way. I'm pretty sure my metallic rattle noise is still there (did one test drive so far and I still noticed it at one point), so perhaps I'll need to further explore the power steering pump "play" here at some point.
By the way, the substitute crank pulley I installed has an updated part number ending in .63, and the difference with the old pulley (ending in .62) is it's a little bit beefier. There is significantly thicker material near the middle, where the mounting bolt goes.
