Success!
While looking at all of the intellipanel "service inspect" functions I must have entered Mode "L" Throttle Sensor Fine-adjustment Mode.
@whitetiger provided the workshop manual info pages 9-S24 through 9-S27 which give step by step instructions for the fine HST and Throttle adjustments. All it takes to enter this adjustment mode is to select "L" and hold the "display mode" button for 2 seconds. My guess is once I entered this "test mode" I had to go through the steps to get out of the mode - although I don't plan on testing that theory. Once it was starting properly I ran the regeneration and now all is well!
Here are the events I did to get up and running again as well as screenshots of the WSM pages.
Based on the debug so far and the comments here everything was pointing towards the HST (throttle) as being the source of my grief. Once I had a WSM I found the pages 9-S24 through 9-S27 fine HST and Throttle adjustments and started the steps. I will attach the pages.
I preceded to follow Mode "K" HST fine-adjustments. While going through this I was getting "Out of Setting Position ERROR No. 71" which has a line item in these steps. I was getting this error because I was in gear "M" and should have been in Neutral (one of the first steps and I failed to do it). Once I had the tractor in the correct setup (brake on, Neutral, etc.) I was able to move to the next step. The rest was straight forward and once completed I tried to restart - but no luck, it still would not start.
Thinking it still could be the throttle I proceeded to go through Mode "L" Throttle Sensor Fine-adjustment Mode. These steps were simple and completed in about a minute. Tried to restart and... hearing that engine kick over was so great to hear!
I immediately started the regeneration cycle and after a few minutes I was back to new.
Thank you everyone for the help - I really appreciate it. I hope I can be as helpful in the future. I plan on keeping my service appointment in February - I might as well have it looked over by someone who knows what they are doing.