Novice to manufacturing - so many questions!

[Infraviolet]

"8 layers, 450 x 420 mm!  I've never seen anything like that in consumer stuff!"
Isn't that about typical for the motherboards in some laptops? Though the manufacturer is likely using one motherboard design fora whole series of laptops with only minor changes between models, or just the soldering on or lack of particular components, so they get a lot of economies of scale.

That said, even then they're well below having 2000 components on such a board, much of the large area being to give more space for thermal considerations and to let the board run right up to the laptop's edges so all the connectors can be on one board and not need separate daughter boards wired to it.

[mariush]

A mATX motherboard is  9.6" by 9.6"  - 244 mm by 244 mm 

450 x 420 is nearly 4 mATX motherboards in a 2x2 arrangement... it's huge.