well i have managed to put the solar system in a near circular orbit around the milky way galaxy, attached in post. i did this without editing any file manually, so it may not be completely accurate.
i noticed that the balance selected tool could be used to put all objects in motion, by firing an object in the opposite direction, and then balancing it.
After a bit of experimentation, i determined that firing the earth at 240 light speeds will get the sun and all its orbiting bodies headed in one direction at 216 km/s.
you can simply fire the earth straight at the ecliptic, at the sun, and then play for a few 24-hour-time-steps, don't worry about hitting anything, the earth will be moving too fast
select all, and then balance selected. play again and you will see that all bodies are in their original orbit around the sun, only just moving at 216 km/s in one direction. 216 km/s is a good approximate for the orbital speed of the sun around the galaxy
delete the dust in the simulation as it does not move, it is unaffected by balance selected. also delete the earth you have fired
next play the simulation for a few seconds until you have trails of reasonable length, it should look like a bunch of winding lines
fiddle with the camera controls so that the trails are now parralel with the vertical direction.
place the milky way galaxy so that the circumference of the galaxy is parrallel to the trails of the solar system (although you won't be able to see the trails now, the screen should be lined up with the trails, giving you a sense of direction)
now click on the sun, and read the sma. move the galaxy horizontally back and forth until the sma reads around 27,000 to 28,000 light years
trails may be buggy and dissapear randomly, to see the trails pause the simulation and toggle t a few times
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at a time step of 1 day, it would take around 8 hours to simulate one orbit of the milky way, which is not too unreasonable, although i can't guarentee that the solar system will behave and stay in orbit