Note dlc characters are not required for the trophy nor is the supreme Kai of time.
To unlock all the characters and variations in the game you must first complete the story including the distorted time eggs and the future gohan mission at the end.
The distorted time eggs are given upon completion for each time rift.
Then summon shenron 4 times, and wish for more playable characters.
You can grind dragon balls using two methods. 1 start a new character, beat raditz and look for the blue exclamation mark on the map, win and you’re given a guaranteed dragon ball. 2 grind parallel quests 4, 23 or 79 and beat the time patrollers for a chance of a dragon ball. If you receive a dragon ball it will say that you got a key item.
Finally complete all parallel quests (I don’t believe ultimate finishes or z ranks are required)
If some parallel quests are missing look for blue exclamation marks on the map or complete the quests leading up to or after the pq and it should unlock more.