Facebook – How to prevent the posts of friends of Friends from showing up in Facebook

Click on the triangle in the upper right corner of the blue bar at the top of the window, then Settings, then Privacy in the left sidebar, and then Limit Past Posts on the right to expand that section. Then click the Limit Old Posts button to limit your past posts to (at most) your friends.

You can also change the privacy setting on each post individually by clicking on the globe icon next to the public post.

To some extent, yes. When writing a post, if you click on the gear icon, you can set custom privacy settings for the post, to include/exclude specific lists and networks.

However, Facebook's About page for the Subscribe Button states:

Subscribers can see only the things you share publicly. They can also choose how many and what types of these public updates they get.

So you may not be able to explicitly include your Subscribers in this list. (I don't have Subscribers set up; you'll have to try it.)