The map (Touchpad) is your best friend, go the wrong way first.
Where there are brackets, I have split the numbers up between sections (loading screens and/or levels).
I've heard in order to unlock the final dungeon you need to complete all intervention quests and side quests (miniventures) before the point of no return (Seraphie should say), prior to this they don't disappear so you can leave them until the end
*** Spoiler - click to reveal ***before the 2nd attempt at fighting the final boss Bahamut, and after you get Tama and all the Pleid back, Seraphie will basically tell you its the point of no return, that said you can still access all the areas after the battles + the new dungeons
For a video guide here is a playlist by factor747 (thanks to shauntmw in comments for posting it)
https://www.youtube.com/playlist?list=PLRdic7wFhHbWI2HY5M_BI...Wellspring Woods - 2
Cornelia - 1 Town and 1 Region
The Nether Nebula - 9 (1/3/2/0/3)
The Watchplains - 9 (3/2/3/1)
Pyreglow Forest - 8 (2/3/1/1/1)
Forest Lake - 1 (thanks to albajos, see comments)
Icicle Ridge Inn - 1
Icicle Ridge - 8 (3/3/1/1)
Saronia Harbour - 2
Saronia Docks - 17 Chests + 2 Mimics (2/15/2)
At the Saronia Docks in the 2nd section there is a treasure ship, to make it appear watch this random youtube vid (note the solution is in game and should only be three rings, so the first one he rings doesn't need to be rung)
The Rainbow Shores - 1
The Dragon Scars - 16 (3/5/6/1SA/1)
Agarthir - 1
Nibelheim - 1
Valley Seven - 8 (3/1/3/1)
The Windswept Mire - 4 (0/3/1)
Caravan - 1
The Phantom Sands - 7 (2/1/1/1SA/1/1)
Underground Prison - 17 (0/0/3/2/2/1/2/2/0/1/2SA/2)
Mako Reactor 0 - 7 Chests + 2 Mimics (3/2/0/4)
Big Bridge - 8
Tometown of the Ancients - 1
The Train Graveyard - 19 (4/3/4/3/5)
Eclipsed Region Train Station to Besaid - 1
Port Besaid - 1 Town and 1 Region
The Sunken Temple - 14 (3/3/3/1/1/3 Intervention quest for big door for last 3 chests)
Nonary Region - 1
The Crystal Tower - 10
The Chainroad - 5 (0/1/0/1/0/3)
Castle Exnine - 27
Balamb Garden - 1
Airship - 1
Ex A - 9 Chests + 1 Mimic (4/2/2/2)
Ex B - 10 Chests + 1 Mimic
Ex C - 14
Ex Z - 1 (very end of level on the main path just before the boss
)