EA knows. But it doesn't want to tell you. Or else it would publish a game manual with such information.
EA wants you to self discover. And to make plenty of mistakes along the way, and to make up for your inefficient progress, to buy SimCash to help speed up your progress.
Unfortunately, I don't recall the exact number of plots. If I recall correctly, I think the final piece takes 22/22/22 of the mountain items to open.
There are players here who could tell you, but it's not like most of us keep track of such information. Hopefully someone else comes by who can help further.
