I do WWI scale and sailboats so I am quite familiar with cable runs. One thing I do with cables is install what I call an idler bell crank. Basically it's another servo arm mounted to the fuselage a few inches from the servo. The cables connect to this arm and the servo drives it with a push rod in the conventional way. Difference is the push rod is only a few inches rather than the entire fuselage and you can tighten the cables up without adding stress to the servo. Also you can service the servo without disconnecting any cables. In addition, Servo City offers a system where you can add a bearing support to the top of the servo. Supporting that output shaft from the outside as well as inside.

Cable runs should be arrow straight and cross once. That is, for a rudder the cable on the left servo arm goes to the right side of the rudder and vice versa. Crossing helps keep everything taught. Some will disagree with the crossing but I find it helps.

Good source for cable is fishing leader wire. I like to use American Fishing Wire products AFW. Comes in all kinds of strengths, coated or not and some colors. Proper sized crimps are also available from the same source. The more strands of wire the more flexible the cable.