By the way, my (very clumsy, but working) start script look like that:
#! /bin/bash
jackd -d alsa --device hw:USB --rate 44100 --period 256 & # Scarlett 2i2
sleep 1
qjackctl &
sleep 1
a2jmidi_bridge &
sleep 1
~/bin/carla2.0/Carla ~/projects/sonicpi/playground/config/carla/audio-test.carxp &
sonicpi &
The (brute force, but working) stop script once I am done and want to revive pulse-audio:
#! /bin/bash
killall -9 sonicpi sonic-pi m2o o2m beam.smp ruby &
killall -9 carla &
killall -9 a2jmidi_bridge &
killall -9 jackd jackdbus qjackctl &
killall -9 jackd jackdbus qjackctl sonicpi sonic-pi m2o o2m beam.smp
Any suggestions how to do this in a more elegant way are very appreciated 
.