For the benefit of future players about to undertake this Series:

This series is a "challenge" consisting of 60 events spread over 12 stages. Most of them use the Porsche 919 Hybrid.  This car has a PR of 90.2 with NO upgrades.   As you might expect, the most difficult events are in the last 3 stages.  I had to use G to skip about 8 of the events.  The most difficult are events in which you are not allowed to go off track.  This restriction makes it extremely difficult to get around the field at the start of the race.  In addition there's an event where you have to reach 220 MPH.  Was only able to get to 218 MPH. 

Unlike a normal career series that unlocks the next one at about 70% completion, a challenge series requires a 100% win completion so you either win the event or pay to skip it.