I'd like to add Cubase 10 to this setup, on a Windows laptop, where C10 is strictly an extra "tone module". In Cubase, I hope to have a few instances of VST's such as Retrologue, Padshop, Groove Agent, etc. There would be no MIDI recorded in Cubase,and there would be no "clock" information sent or needed in Cubase. The XF would be the total master in this scenario. Program changes would be sent from the XF also.

Is this possible? What steps do I need to take to set this up.

Yes, it is possible. You'll need an audio interface and the appropriate cables to connect the XF, audio interface and the computer.

The XF will be your controller and a Tone Generator source.
The Audio Interface will take the XF signal an route it to the computer, and take output of the computer and route it to your sound system.
The Computer will run the DAW software which will host the VSTi

You will want to use Clock information (it is simple enough to configure). Reason being, Groove Agent is like the ultimate Drum construction tool... with configuring for Clock you'll be able to use Tempo driven Effects, LFOs, even run Arpeggios with perfect sync. Might as well setup for Clock, you never know...