There are 45 events - 42 Trophy + 3 TT - with each car having a specific 2-event Showcase + TT.  Only the Divo can be upgraded enough to open the last two cup races (PR90, PR92).

Any single car can reach 75% completion if upgraded to a little under PR81.8 or more...

Gold progress rewards are:

25%  -  8GC
50%  -  13GC  [PR <80.4]
75%  -  18GC  [PR <81.8]
100% -  28GC