Only send updates of position of the players that are likely to be visible ?

Look at railway maps in Tokyo

Or if you are too lazy to search, https://youtu.be/3NfUAO_KjQA

It is both, but the pressure one contributes more to lift. You can see this when a wing stalls, the airflow separates from the upper surface and the pressure difference is gone. The angle of a stalled wing still means air is directed downwards, but the overall lift is much smaller.

At least that is what I’ve been told anyways

Wait til you get stuck in a traffic jam