A bit more complicated than that - try it on
https://coriolis.io/
Your ship's total mass is the sum of the hull mass, all the modules' mass, fuel and the cargo mass.
Your jump range depends on the ratio between the
FSD's optimal mass and the ship's
total mass at the time you charge up for the jump. If you use the route plotter, the plotter assumes a full tank for all jumps on the route.
Your shield strength depends on the ratio between your ship's
hull mass and the
shield generator's optimal mass (and a fudge factor, which is why some ships make good shield tanks, while others don't).
Engineering a module only affects that module's stats - so enhanced low power reduces the shield generator mass as well as the shield generator's optimum mass. The first one will also decrease your ship's total mass, giving you a better jump range. The latter will decrease the shield strength if your ship's hull mass is over the shield's optimum mass. Since ELP also increases the shield's optimum strength, you (usually) still come out ahead of the game.
A lot of modules also have a maximum mass - that's the maximum mass they will handle.
Since you wanted maximum range - here's a quick-and-dirty example for a DBX:
https://s.orbis.zone/iv_8 . No scoop, as >400 ly range will get you anywhere in the Bubble. If you want enginnered thrusters, you'll need a differently engineered (or just bigger) power plant.
As for fun, though, I also cobbled together a Hauler:
https://s.orbis.zone/iv_g . Added a scoop this time - and engineered enhanced performance thrusters

. Still ample power left over, but you just can't fit a smaller power plant. Also cheaper than the DBX, so easier on the rebuy - or for the ship transfer. The only issue is that the Hauler tends to run a little hot, especially when scooping, so I also added some lightweighted heatsinks (for peace of mind, mostly - ED's ships are hard to destroy simply from overheating).
Assuming a 400 ly trip, the Hauler will need two more jumps and one scoop - but will also idle faster than the DBX can boost. Of course, you could also engineer the DBX's thrusters, but that'll cost you power and mass, decreasing the jump range. The balance is up to you.