I know this doesn't address your question, but this is one of the reasons that I like working with VST plug-ins, which makes it very easy to do various things that would be hard on hardware.

I wonder if you can layer two voices in your hardware and control the strings/pads with an expression pedal.

I’ve always liked Yamaha PSR keyboards for this reason – you can actually play piano with strings comfortably, using a pedal. Some other keyboards at least have an option to ignore the pedal for dual voices, but it’s not quite the same.

In general where the parameters attack, decay and release determine the time...

Thats where with sustain the parameter eddits the level as the time of sustain by default is set bu how long you hold the key...

I know the BK-5 lets you adjust which voices are affected by the sustain pedal. I think this is one of the first mid-priced arrangers from Roland that permit this fine level of control.

Yes explore the manual. Don't just skim it, actually sit down at the board and go through the menus. It's amazing what you'll discover, and you'll notice things that will make a huge difference in your musical results!