Trying to understand pipewire jack emulation better

Hi list,

having used jackd for more than a decade, I am now wanting to give
pipewire a try and, of course, use its jack emulation from the Debian
package pipewire-jack in addition to pipewire-alsa and pipewire-pulse.

So far my installation works fine with my laptop's internal card, mpv
outputs audio via pipewire nicely, but the following questions remain,
perhaps someone can help me further here?

For software requiring jack I find that the pipewire installation will
not provide a running jack server per se, but that I have to start one
with jackd or qjackctl. I am puzzled here because qjackctl has its own
settings for devices, samplerate and buffer size and so on. (How) will
they be respected, or are they simply ignored by the pipewire jack
emulation?

How can I tell pipewire to use a different card, eg. an external USB
card instead of the built-in one?

How can I tell pipewire to use a specific sampling rate and buffer size
for a given card? I know that I can set the buffer size for the jack
emulation by prefixing an application with 
	PIPEWIRE_LATENCY="128/48000" application

Is the settable "quantum" for midi buffer/latency only?

What would I be using wireplumber for if there is a GUI connection manager
such as qpwgraph installed?

Here is some info on my system:
$ inxi -A
Audio:
  Device-1: Intel 82801I HD Audio vendor: Dell driver: snd_hda_intel v: kernel bus-ID: 00:1b.0 chip-ID: 8086:293e
  API: ALSA v: k6.12.90+deb13-rt-amd64 status: kernel-api
  Server-1: JACK v: 1.9.22 status: off
  Server-2: PipeWire v: 1.4.2 status: active with: 1: pipewire-pulse status: active
    2: wireplumber status: active 3: pipewire-alsa type: plugin 4: pw-jack type: plugin

Thanks!
Peter