Please share the answer to #2 ... because after several attempts I did not manage to start and setup pulseaudio on windows
I gave up on pulseaudio, couldn't figure it out. Here's how to route the audio in windows:
1) Just start DSD-FME using -i /dev/dsp, or don't specify `-i` at all.
2) Open the windows sound mixer. (Windows 11: Settings > System > Sound > Volume Mixer).
3) Find DSD-FME and set the input device:

Change it from default to whatever input you'd like to use.
4) Important: Restart DSD-FME!
This worked for me.
For Multiple instances of DSD-FME: (Examples using 2 lines: VAC Line 1 and VB-Audio Cable)
1) Copy the DSD-FME executable, and give it another name.

2) Run both copies, using -i /dev/dsp. Here called dsd-fme.exe and dsd-fme-2.exe.
3) Open the volume mixer and set the desired input device. Here, dsd-fme.exe is set to VB-Audio Cable, and dsd-fme-2.exe is set to VAC Line 1.

4) Restart both instances of dsd-fme, and you should get separate input to each instance.
Here is a screenshot of the setup, using SDR++ with two VFOs. `Radio` is parked on a P25 channel, and is sending its audio to dsd-fme.exe via VB-Audio Cable. `Radio 2` is parked on a Con+ control channel and is sending its audio to dsd-fme-2.exe via VAC Line 1.

Hope this helps!