I'm going to safely assume the front half will not be waterproof anymore as the adhesive has been split from the frame/digitizer. The back half should be okay since it's using the tightening pressure of the torx screws to keep it sealed.
For step 4, the connection to the battery should always be done as soon as possible so after removing the back plate to the board would be ideal.
Otherwise, very thorough so far!
Oh be patient mate, they JUST got this brand new. Splitting the display from the glass will be one of the trickiest projects while preserving the LCD. The idea of keeping the lightning port a solder on was definitely a major flop. I don't see why that needed to be but now this'll be a repair for the lesser. 2/10 sounds about right.