PCB with multiple Arduinos and onboard hub
The first question would be guessing, so I leave that to (electronics) professional people.
The capacitors are used to have some small 'energy storage' to compensate fluctuations. The Ferrite beads/inductors are used to improve EMI/high frequency reduction. It seems the analog part of the GL850G uses 3.3V.
These capacitors are for the same reason as in 2. These are called bypass capacitors, sometimes multiple values are used.
In principle it does not matter where the voltage comes from, but connect all GND's together.