The important thing to pay attention to here is that is says that you have to get A STAR in every event. So you don't have to win every event you just have to get at least one star so come in 1st, 2nd or 3rd. There are no requirements in the game to 3Star every event so don't fret over that if you don't have to. (Some of the Skill Checks require 3 star completions of specific things so be sure to check the Hall of Fame section for those specifics)
Also this only pertains to the EVENTS. The championship races are not a requirement of these.
There are 5 event types with 20 tracks so this is a 100 event completion.
The Races are self explanatory. Come in 1st 2nd or 3rd.
The Battle Races are same as regular races but with weapons. Come in 1st 2nd or 3rd.
The Stunt Races, generally on easy the opponents don't get over 9000-10000pts so just get to that score and you could probably just set the controller down and let the timer run out.
The Takedown Races require that you get through about 4 waves maybe even 3, get about 2800pts and again you can just let the timer run out.
The Best Lap Challenges, just do 5 laps on each and the 1 star time is usually easy.