If you're trying to get this before the game closes (in a month), I'd advise several things to do:
- Remember that to complete a chapter you have to 100% each Event in each Part of each Episode
- Upgrade cars that are 4+ stars, ignore 2/3 star cars!
- Only upgrade 1 of each car type per colour, the rest is a waste of items & money
- The most important cars to upgrade are Classic!
- Play the Car Shows as often as you can (the exhause symbol on the right of the tabs)
- Play the Spotlight races every day, as far as you can
- Grind Episode 1, Part 4, Event 4 (bottom row, red, blue & yellow cars) as much as you can to get extra Challenge cards, make sure to go as high on difficulty as you can
- Play the main races as soon as you can (with a bit of a power difference over your opponent)
- Use Auto-Race as often as you can (as long as you've already got the Would You Walk achievement), it saves time - you need 20+ power over your opponent
- Save your Gold Credits for paying for money - it's the hardest resource to get, cars come easy, cash doesn't
- Save your Upgrade Cards for Class Upgrades, unless you run out of Pro Upgrades, but DO NOT buy regular Upgrade Cards!!!
When they announced the shut down I hadn't even completed Episode 2, so grinding for just over a month got me through 2 & 3
Cars you need for each Part of Episode 3:
Part 1, Event 1 (507-529): Green, Yellow, Yellow Classic, Red
Part 1, Event 2 (515-534): Green, Green Classic, Yellow Classic, Blue, Blue Modern
Part 1, Event 3 (520-538): Yellow Classic, Red, Green, Green Classic
Part 1, Event 4 (519-543): Green, Green Modern, Yellow Classic, Blue, Red, Red Modern
Part 1, Event 5:(527-547) Yellow, Yellow Modern, Yellow Classic, Green, Blue Classic, Red Classic
Part 1, Event 6 (532-552): Yellow, Yellow Classic, Green Classic, Blue Classic, Red Classic
All cars needed:
Green, Green Classic, Green Modern
Yellow, Yellow Classic, Yellow Modern
Red, Red Classic, Red Modern
Blue, Blue Classic, Blue Modern
Part 2, Event 1 (526-546): Red, Green, Green Classic, Yellow, Yellow Modern
Part 2, Event 2 (534-552): Green, Green Classic, Green Modern, Blue
Part 2, Event 3 (540-558): Blue, Blue Modern, Red, Green Classic
Part 2, Event 4 (546-565): Green, Green Classic, Yellow, Red
Part 2, Event 5 (553-571): Yellow Classic, Blue Classic, Green Classic, Red Classic
Part 2, Event 6 (559-577): Green Classic, Red, Blue, Yellow
All cars needed:
Red, Red Classic
Green, Green Classic, Green Modern
Yellow, Yellow Classic, Yellow Modern
Blue, Blue Classic, Blue Modern
Part 3: Event 1 (551-577): Yellow, Yellow Classic, Green, Green Classic, Red, Red Classic, Blue, Blue Classic
Part 3, Event 2 (564-583): Blue, Blue Classic, Blue Modern, Red, Yellow Classic, Green
Part 3, Event 3 (571-589): Blue, Blue Classic, Red, Red Modern, Yellow
Part 3, Event 4 (576-595): Yellow, Yellow Classic, Yellow Modern, Green, Green Classic, Blue Classic
Part 3, Event 5 (589-601): Green, Green Classic, Blue, Blue Classic, Red, Red Classic
Part 3, Event 6 (591-607): Blue, Blue Classic, Green, Green Classic, Yellow, Yellow Classic, Red, Red Classic
All cars needed:
Yellow, Yellow Classic, Yellow Modern
Green, Green Classic
Red, Red Classic, Red Modern
Blue, Blue Classic, Blue Modern
Part 4, Event 1 (589-604): Red, Red Classic, Green, Blue Classic
Part 4, Event 2 (592-610): Yellow, Yellow Classic, Green, Green Classic, Green Modern, Red, Red Classic
Part 4, Event 3 (601-616): Yellow Classic, Red, Red Classic, Blue, Blue Classic, Blue Modern
Part 4, Event 4 (603-623): Red, Red Classic, Yellow, Yellow Modern, Green
Part 4, Event 5 (611-629): Red, Red Classic, Red Modern, Green Classic, Yellow Classic, Blue Classic
Part 4, Event 6 (612-635): Red, Red Classic, Green Classic, Blue Classic, Yellow Classic
All cars needed:
Red, Red Classic, Red Modern
Green, Green Classic, Green Modern
Blue, Blue Classic, Blue Modern
Yellow, Yellow Classic, Yellow Modern