Price difference between buying and selling through the Captain’s Cabin or the shops

The Death Vessel and Crusader/Florintine pack are included as well, but dlc like the ones that unlock everything in multiplayer and the ones that unlock the whole map and stuff are not.

100% sync within AC4 is not dependant upon everything available ingame. Especially the present time stuff is not required.

To check which points are missing, it is most advisable to check the "progress tracker" ingame, which mentions the side objectives which have to be completed to achieve 100% sync. 100% completion is solely tied to everything mentioned in this progress tracker.

These include all the different collectibles (Animus fragments, chests, secrets (which includes manuscripts and letters), viewpoints, shanties and the Mayan stones). Also required are the unlocks of all taverns, the defeat of the 4 legendary ships, the liberation of all forts, the completion of all assassination & naval contracts as well as the templar hunt missions.

Of course, 100% sync in all storyline missions is required as well. :-)