I was looking at the FAQ to see when certain Homestead missions unlock and it seems like some should already be available but they are not. For example, I'm in Sequence 8 and the first Manor Mysteries and the mission with the Innkeepers should be available but I haven't seen them. Maybe there are some I haven't done yet?
If you've done all the previous missions, the new ones will pop up according to that schedule. If you haven't done all the previous missions, they'll pop up when you've finished the required one before it.
And do remember--not all Homestead missions start in the Homestead. You get the farmers and Big Dave in the Frontier, and the tailor in New York, and I think there's another in one of the cities.
Look everywhere for the symbol. It's possible to miss them when you're focusing on the main story in the cities.