EA was set up as part of the Dieselgate settlement. The settlement stipulates, that EA must not give special treatment to VAG. It's run at arm's length from the rest of the group.
The current Taycan (and its sibling, the Audi e-tron GT) is built on the J1 platform. PPE stands for Premium Platform Electric and is the next generation platform jointly developed with Audi. It will debut in next year's Porsche Macan. As I understand it, the current generation Taycan will not...
Has to do with the computing architecture. Tesla started with a clean slate and designed the system from the ground up to be OTA capable. VAG did the same thing for the MEB based vehicles (ICAS based). For Porsche this will arrive with the PPE based cars, e.g. the Macan EV.