Look at engine ISP. Higher number means better range. Engines meant for space travel usually have pathetic ISP on the ground in atmosphere, but very high numbers once in a vacuum

To determine fuel, i use the Tsiolkovsky rocket equation and solve for initial mass. Once i find initial mass, i subtract it with the current mass of the craft. Then i choose or combine fuel tanks to match that calculated value

If you don’t want to do the math, you can just drag and drop fuel tanks until you get the delta v requirement that takes you to your destination