Help me choose my first spindle

[Ger21]

option 3. Via Mach3 which talks to the VFD through an interface board. This can be added later so again don't need to worry about it in terms of spindle selection. My understanding here is that this can be PWM signal or a 0-10V signal.

Mach3 or LinuxCNC outputs a PWM signal, which is then converted to 0-10V which is fed to the VFD. You need a spindle controller or breakout board that does this. You can also get controllers that convert step/dir to 0-10V. Someone at CNC Zone just used a step/dir signal to a Hitachi VFD to control it directly.
You can also use Modbus to control the VFD.
Lots of different options.