I'm making slow but steady progress. My mechanic still has not been able to fix the codes so I can get the vehicle smog-certified.
I replaced the too-far-gone front headlights, and discovered that the right-side headlight bracket & socket connector were held together with bits of tape. I'll need a new one of those... Replaced the CD holder with a shelf, removed the ash-tray, fixed the roof retract mechanism, replaced the fuel-fill sensor (seems to have helped making filling easier), added many plastic fasteners to the trunk & hood carpets, replaced all the hood / trunk struts, and on and on.
I'm thinking I may need to head to an official Porsche dealer to sort out the smog certificate issues. I've attached an OBD report, in case anyone has any suggestions.