Nice one!
I remember doing my 996 Gauge Cluster & OBC upgrade (so I know how you feel
). It took quite a while to gather all necessary information and materials (i noticed that the recommended wires for the 996 Gauge Cluster were not "perfectly" fitting, but figured out, which were the right ones for my MY2001), and to exactly understand what you are doing. I used the same books and forums just like you did.
BTW: I was able to do those upgrades, without any soldering (used "Posi-Lock" connectors, which are perfect) and without removing the steering wheel (you can attach the OBC-stalk switch "easily" from the left side).
Only thing i wasn't able to do is the cruise control, as there is no valid information on how to do the connection on a MY2001 car with a 2004 996 gauge cluster: Motronic or Gauge Cluster?
But actually i can live without the cc