FYI the definive thread on installing a 800W spindle is here. LOTS of great information there. This is about a water-cooled version installed on an HDZ though, so not everything applies.
I have the feeling that the stock Z will struggle to cope with the extra weight, you may be able to get away with it by adding stiffer or extra springs to compensate for the extra weight, but I feel (personal opinion) that it’s asking for trouble, at least as a permanent solution. A Z-plus would take it easily (and a HDZ too, oobviously)
There are a few threads on how to interface the VFD to the Shapeoko controller, it boils down to connecting the PWM and GND signals to your VFD. Your shapeoko from Feb 2019 may not have the 6pin connector sticking out of the enclosure? So for you to access this signal you may have to go and solder pin headers on the controller.
If you are mainly after noise reduction (which was my driver to move to a spindle too), did you consider a water-cooled one? It’s even quieter (but admittedly comes with the extra burden to install the cooling lines)