/usr/bin/fluidsynth is an executable. by default, launching fluidsynth from the commandline will bring up a shell, but you also have the option of using config files, as well as passing many other commandline arguments. check 'man fluidsynth' ... you should be able to setup it up as you like, then just have it as a startup application or make a simple script with the proper commandline arguments and config. you can disable the shell mode to, so that it's non-interactive and just launches and runs in the background, as well.
you should be able to run it similar to timity++