I've only done 3. (Only. haha) They were Hard, Hard+, and Survivor+.
I've been mostly playing the MP since completing the game my first time.
I've actually been wanting to go through the game a 4th time, but I'm thinking I will finish getting the Platinum and take a break for awhile, before I do that. (and await for the DLC.)
I want to move on to some of my backlog.
Do you to beat every game mode and get all the achievements to get platinum? Also you have to do 12 weeks on mp with hunters and fireflies?
Yes, you have to get all the other trophies, before you get the platinum.
You only need to beat the game a minimum of 2 times, in order to receive all the difficulty related trophies.
The rest of the trophies are related to the artifacts/goals in the game: (Documents, Comics, Firefly pendants, Shiv doors, crafting, etc.)
And yes, you need to complete 12 weeks on both Hunters and Fireflies MP.