The usual extra info on this series for the McLaren Senna GTR, plus McLaren P1 GTR and Ferrari FXXK EVO...
There are 51 events (48 Trophy + 3 TT) with each car having a specific two-event showcase + TT. The rewards 25-50-75-100% are split 10-15-21-33GC, with only the Senna able to be upgraded enough to complete the series
With just the P1 GTR (or FXXK) you can reach 75% without being fully upgraded:
With both of them, and at least one being fully upgraded you can do all but the Senna's showcase/TT and the last two cup races:
The upgrade details for the Senna GTR can be found here