How to recieve data over SPI as a master device?
There is no difference.

The CS is always from master to slave, as master is the one that generates the clock, and slave always listens for the clock (and it basically is gated by the CS).

Basically when the master transmits a byte to slave, it also receives a byte from the slave.

If you want the master to receive data from slave, the slave must set the byte into data register for transfer, and the master must transfer dummy bytes to clock data back from slave.

While it is possible for the devices to arbitrate who is the master and exchange roles, multimaster SPI implementations may not be the easiest to start with. It just is easier to have one board as master, and one board as slave.