To do this you must be al least 24 Lvl and then you will be able to purchase all tracks. This will set you back around 10 million credits. After every track (yes, also reverse variants) has been purchased, you have to get a gold medal on each one of them (yes, also reverse variants).
From what I have found online, AND MY PERSONAL EXPERIENCE you can use different cars, different mods and even do some drifts and some time attacks, as long as you get a gold medal on every map.
Time attacks seem to be a lot easier to get gold medals, so you could just try get all golds in time attack, but I suggest start by finding your favorite drift car (don't forget to install Drift or Ultimate mod), then get as many gold medals on different maps in drift events, then do the rest of the maps in time attack events. That way you will learn to drift and get a lot of credits and also work on distance traveled achievements.
Note: After I got gold medal on every track (most drift, the rest time attack), my achievement did not unlock, but it unlocked when I got a gold medal with different car on a track I already had a gold medal.