The usual extra info on this series created for the Vantage 59 but also including the Carrera S and 458 Italia...
There are 51 events (48 Trophy + 3 TT) and the rewards 25-50-75-100% are split 8-13-17-27GC.  You will need all three cars for 100% and only the Aston can be upgraded enough for the final cup races.
For 75% you'll need two cars, one of which is upgraded to around PR47 - tiers open up well in advance so you can get there with non-cup events :

The Aston needs to be upgraded to 5444433 to complete the series (in gold 390GC more than the all 3's required to win the LTS)