It's best to split this achievement into three parts based on overall difficulty and when in the game you are likely to finish them:
1. Weapons and Gadgets - There are 24 weapons and 16 gadgets in the game, which are more than what is required to get this achievement. The True Achievements walkthrough has details of where to get all of them (Crackdown 3: Campaign Walkthrough
2. Orbs - There are 750 agility Orbs and 250 hidden Orbs in the game. You will collect most of these as you progress through the story. The best guide I could find on the exact location of every single orb is by SerThicc, who has created a series of maps split into districts (https://imgur.com/a/KxSF8eV
3. Races - There are 15 road races, 17 agility races and 7 wingsuit races in the game. You will need level 5 agility and driving to unlock all of the races. The agility and wingsuit races are not too difficult to complete but you may need to complete the route more than once in order to learn the layout. Road races are very difficult, but not impossible, to complete. The cars in this game have a lot of oversteer and can flip easily when you make contact with objects. Also, unlike with the agility and wingsuit races, you will go round a circuit twice.
If you want to watch someone doing the races reaching the times to get gold, cakechieveables has a series of videos showing the exact route to take for everyone single road and rooftop race and Simplup has created a video for reaching gold on the wingsuit races:
Road Races -
Rooftop/Agility Races -
Wingsuit Races -