You can't use the air brake to stop the spindle, when using a VFD you will burn it up, but you will need your brake, to hold the spindle when you change the tools
The VFD if you want to stop fast, then you will need a Breaking Resistor, this has nothing to do with what size the VFD is or the motor Hp, you have a lot of spinning mass, in the head of these machines, so if you want to stop fast, then you will need a Braking Resistor, any general purpose VFD will do what you need
To help slow the spindle down you can use some DC Braking, this is a parameter you can set in the VFD