FB messages are implemented in the messaging app, just like in N9.
Yep, the N9 had a different kind of screen which made the low power mode / clock etz. possible. The same isn´t technically possible with Jolla´s screen, although an Android type Glance-feature might be possible.
What do you mean by "support notification"? Update notification for the app or notifications when a message is received? The latter do exist, but at least at the moment you have to have whatsapp open for them to appear.