SPI Timing of WIZ850io
If you research a bit more, you will find, that you need to have a look at the W5500 datasheet for a full specification.
This will contain:

Which should answer your first question.


This might be a misunderstanding, for powering up you'd have to look at the power on sequencing or reset timing. You need to understand the SPI timing diagram to understand how to set up your SPI communication correctly.




Yes.



It allows you to share the line with other devices. Which is typical for a SPI bus. You can connect several slaves, so when one slave is not addressed (with the CS) it has to free the bus putting its MISO pin in HI-Z.