how to get all characters

you will need gold trophies
1 gold = 2 silver = 4 bronze
1 silver = 2 bronze

Koopa = 1 original gold trophie
Waluigi = 3 original gold trophies
Shy Guy = 4 original gold trophies
Birdo = 6 original gold trophies
King Boo = 8 original gold trophies
Hammer Bro = 10 original gold trophies
Dry Bowser = 11 original gold trophies
Petey Pirahna = 12/13 original gold trophies
Link = 14 original gold trophie
Bowser Jr. = 1 custom gold trophies
Rosalina = 3 custom gold trophies
Diddy Kong = 4 custom gold trophies
Dry Bones = 6 custom gold trophies
Funky Kong = 8 custom gold trophies
Toadette = 10 custom gold trophies

And all the caracters I unlock is Bowser Jr...

I think this is wrong, I unlocked Petey with 12 gold trophies
Also you forgot Funky and Toadette

So, basically:
Gold in every base cup
Gold in a bunch of custom track cups.

10 custom track cups I think

because I don’t have them yet

There are some tracks you can use to grind the custom ones. Basically, the computers can't finish them so you get infinite gold cups.
https://mkpc.malahieude.net/circuit.php?mid=2270

thx

Thanks !