I'm in the middle of chapter 6, after about 160 hours. I've been doing every optional mission, stranger mission, stranger encounter, camp item requests, moving event mission, and stranger interaction.
Although I've done most eatser eggs, hissen sites, and four of the item collection quests (dreamcatchers, gunslingers, cigarette cards, rock carvings), and progressed somewhat on challenges and other things required for 100% completion, I'm mostly leaving those things for after-story game play, because I don't actually intend to play through the main story more than once.
My plan is basically: go through the story once only, doing every side quest as I go, in white hat mode before online comes out. Then, post-story, do all the requirements (collectables, challenges etc) for the 100% and all other achievement trophies very slowly over time (in black hat mode), as well as checking off any remaining Easter eggs. Slowly, because post-story I intend to sink my time mostly into online for a while.