Theoretically, I am trying to launch a rocket from space and trying to figure out how much fuel I would need to get to a certain distance.
There is no limit how much distance a rocket can travel once it has exceeded escape velocity. So there is no simple relationship between fuel and distance.
Voyager 1 ran out of fuel many years ago, but is currently traveling at a speed of 17 km/s (11 mi/s) relative to the Sun. It will continue traveling at this speed for the foreseeable future and will be at a distance of a lightyear in about 18,000 years.
Newton's first law says that in the absence of forces, a body in motion will continue with that same motion indefinitely. When there is gravity, once a rocket exceeds its local escape velocity it will continue traveling forever.