The rest is simply up to you how much more detail you wish to add.  You could create a helix, or wrap a strip of quads between the buttons to create a thread, etc.  You could select a ring of edges on the outter edge of the button, bevel them inwards slightly, and create ridges on the button, whatever you want.  It should unwrap easily for texturing even with the level of SubD, or you could unwrap it before you subdivide to make texturing as easy as possible.

Hope you found this useful.  If you're a beginner at modeling, this might be a good way to get to know your edge loop tools, and how to punch holes in objects without using sloppy boolean functions.  Good luck! ;)

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