Welcome deepfraught 
The red/spring/black assembly and the black hemicycle are parts of the quick release seat molding.
Quick Release Seat Molding ST-QRS-001
quickly removable seat pin / QRS modification DIY
The silver rod inside the spring is the very important “seat-pin”.
This pin must be screwed in the seat tube, inside of the seat molding!
Otherwise the seat (including molding) might slip downwards under load.
You didn’t really remove these parts from the seat molding…or did you??
Your EVO was not equipped with the quick release seat molding?
I’m just wondering because all pics of the Australian EVO are showing it?
As said above, the plastic hemicycle (locking lever safety/Strida part nr. 322-4-2) is the securing piece for the red locking lever (p. nr. 390-1) of the QRS molding,
images of the parts and mounting advice are here:
QR seat manual .pdf / 8 Mb
Plastic dome nuts are commonly used to cover the thread ends above the steel nuts at the usual (older) plastic seat molding (without quick release system).
I guess the plastic tie is intended for fastening the CD cover and the manual onto the Strida, once it is going to be sold without the box…