Yes Apple build quality is high, but it's not perfect. It's an iron law of electronics that heat shortens lifespan, so taking a large surface that is used for heat dissipation and putting your screen directly on top... I wouldn't do that with mine but you do you.
Don't have a macbook, but on KDE that's already the default anyway it looks like--it's an opt-in to also sleep on lid close when there's an external display connected.