(There are no car-specific events, so only one car is actually necessary to complete the series)
There are 44 events - 33 Trophy + 11 TT - shared across eleven tracks, with each track hosting three Trophy events and a TT. You need to complete 2 Trophy events on a track before its TT will open, and all 3 Trophy events before the next track will open up.
P.S. There are a couple of copy/paste errors on the TT headings:
PR52.8 from the Daytona 500 SE (tune 8-8-2-6 M$ only) will get you past 75%, and full Daytona M$ only tune (10-10-2-6) reaches 88%, but then some GC spend is needed to reach 100%. With full tune either Driver 2 & TP 6 (72GC) or Driver 3 & TP 4 (76GC), but obviously there will be many other permutations depending on your own preference for Tune:Driver:TP spend.
Progress Rewards split:
25% - 9GC and M$9,000
50% - 14GC and M$14,000 [<PR50.3, part way through Indy Road tier]
75% - 19GC and M$19,000 [PR52.3, Richmond tier]
100% - 30GC and M$30,000 [PR55.2]
FYI winning the final 20-lap Daytona Speedway race yields M$100,150 / Driver XP 4,123 / Fame 6,100.
