SPI - fundamental API questions

[Deouss]

After reading a documentation I am still a little confused about SPI
My questions:
Are there any differences between HSPI and VSPI ?
What is maximum speed of SPI?
What happens if different pins are used than native pins?
Also very important - how bits are stored in bytes - particularly in rx_data buffer and how those bytes are put in memory?
rx_data[0] stores first received bits starting from msb or lsb is rx_data[0] first or last data ?
Also same question goes for rx_buffer. There are macros as I see but I am not sure where to set them up.
Additionally - super confusing - what is api difference between spi_common and spi_master ??
There is no clear guide for that.
I would appreciate help with explaining all that.
Thank you