I have done that in the past. I haven’t done it in a couple years. No particular reason I stopped, other than I go through phases of spending a lot of time on “sound design” and then phases where I’m just not interested in detailed sound design because there are billions of presets available.
My solution for the “way more VST parameters than knobs on my controller” was to write a GigPerformer extension to allow “bank switching” of how the controller’s physical knobs/buttons/faders map to widgets.
Just to illustrate as simply as possible, let’s say I have a controller with 9 faders. If I want full control of a B3’s drawbars I need two separate banks of 9 faders (one for upper manual, one for lower). I’d set up a rackspace with two sets of nine faders and map those to the VST parameters. I refer to that as two banks of nine faders.
In the extension I put the logic that allows me to freely switch which of those two banks my controller is actively linked to.
Once that works well the next problem is being able to tell which bank of faders you’re actually currently connected to. I set my extensions up so that there is visual feedback on the GP screen and visual feedback on the controller (to the extent possible depending on the controller).
See Novation SL-MK3 Extension - GP Extensions for example, or MCU Protocol Control Extension - GP Extensions
As a practical matter, I choose my controllers based on how well they can accommodate this kind of thing, rather than trying to force an approach like this onto a controller that just isn’t very compatible with the idea.
For me the critical elements are that knobs must be “endless” and the controller must have at least some type of display. If I’m bank switching through 6 sets of knobs I’m never going to remember that LFO 2 shape is on bank 2 knob 5 for example. The SL-MK3 works well for this, as do many of the MCU-compatible controllers (I’d recommend the iCon P1-M).
If you really want to map out every significant parameter on the Diva you’d need somewhere around 10 knob banks (assuming a controller with 8 knobs per bank). That’s a lot to maneuver your way through, so I think good visual feedback on the controller is very important.
This can all be done through OSC as well, but I generally prefer physical controls to a touch screen.