Also, the Vader reconstruction scene was inconsistent with the OT in that Vader was shown to have no problem breathing without his mask. In ROTJ we're told he'll die without his mask.

He was leeching from the dark side in order to sustain himself on Mustafar. However, it wasn't a permanent solution. It took immense focus and energy. To have that focus broken for a few minutes is fatal (also explains why Vader was able to survive without his mask intact in TFU after his duel with Galen Marek). That's why the medical chamber wherein the reconstruction took place was pressurized, acting as an "iron lung room" of sorts, just as the meditation chamber we see in ESB was pressurized.