Currently I am using the Pisound as a sound source and am running fluidsynth and soundfonts (e. g. to have a Fender Rhodes sound available). It is possible to boot it without attached screen and automatically run an application such as Modep or Pure Data (e. g. with Automatonism). I have not yet figured out how to start and configure fluidsynth but that should not be a problem. You can control the Pisound via a multi functional push button, VNC, bluetooth app and/or TouchOSC but I am rather thinking of using it as a simple box which receives midi and returns sound.
I have some other components I would like to integrate: a hardware mono synth (example with SP sequenced Midi) and another Raspberry-based box running sequencing software (example with a sampling software called cheat codes controlled by a grid). In the center there will be my laptop running a live coding software (be it Sonic Pi or Tidal) which will/should be the master clock. Last but not least I have my guitar (I have recently begun practicing again) which I would like to use in future… 
I am still very much experimenting but it is not only - and I guess only to the least part - a technical issue but rather a question of what music I want to make, where I want to code, to control sound or to play the guitar and how the different parts will work together to compose this music.