If I am missing anything I would just love to get a hint or suggestion.
Be aware that if you PL chain both BL5 and the BL3 you will end having the same channel in one of the BL5 and the BL3!
That’s the same between the PL of the switch and the BST.
for 3 speakers connected to the BST you need minimal two PL cables if every speaker should have its own channel playing.