There are 18 base game chapters (12 main story + 6 new adventures) with 10 minikits each, for a total of 180 minikits. You need to finish all missions on Story first, then mop up in Free Play so you can use the extra characters unlocked from Story.
The TA walkthrough is already a great resource for finding them all, so here it is.
LEGO Star Wars: The Force Awakens WalkthroughIf you'd rather use videos for help, here you go, courtesy of Camzillasmom on YouTube. Sorry it's the PS version, but I like her voice and she's funny sometimes. I made links instead of making this page load 18 videos:
Main StoryPrologue - The Battle of Endor
videoChapter 1 - Assault on Jakku
videoChapter 2 - Escape From the Finalizer
videoChapter 3 - Niima Outpost
videoChapter 4 - The Eravana
videoChapter 5 - Maz's Castle
videoChapter 6 - Battle of Takodana
videoChapter 7 - The Resistance
videoChapter 8 - Starkiller Sabotage
videoChapter 9 - Destroy Starkiller Base
videoChapter 10 - The Finale
videoEpilogue - Luke's Island
videoNew AdventuresPoe to the Rescue (
D'Qar) (need 10 gold bricks)
videoLor San Tekka's Return (
Jakku) (need 20 gold bricks)
videoRathtar Hunting (
Twon Ketee) (need 30 gold bricks)
videoThe Crimson Corsair (
Kerroc) (need 40 gold bricks)
videoTrouble Over Taul (
Taul) (need 50 gold bricks)
videoOttegan Assault (
Arthon) (need 60 gold bricks)
video* gold bricks needed are inclusive, so you need 60 total to access all 6 missions *
Yes, there are 30 extra minikits in the 3 DLC missions. They do not count toward this achievement.