So far I know I am going to use FPP with a FPD; I'm not clear on what comes next in the chain between FPD and lights
You have all kinds of choices.

From the FPD you can connect up to 12 universes. The universes can be any mixture of DMX and/or Pixelnet networks. From the FPP you can ALSO send our E1.31-connected universes.
On the receiving end of the DMX universes you can have DMX controllers -- dumb string controllers, 110v -powered incandescent or LED strings controllers like LOR or Lynx Express, etc.
Yes, you can find smart tring controllers that use DMX.On the receiving end of the Pixelnet universes you have Pixelnet controllers, like DLA Smart hubs, DLA Zeus controllers, Falcon-8 or Falcon-16 controllers, or the upcoming Falcon Smart hub.
If you use hubs, then you still need to connect controllers after the hub.
The strings of lights connect to the controllers. The controllers interpret the DMX or Pixelnet protocols and convert the data into pixel data to drive the smart strings.
Connected to the