Those line diameters should be good. Length depends. Some C/L sports have lengths determined in the rules. For sport and aerobatic flight it is more like whatever gives you lap times and line tension that you like. For aerobatic competion flying, people seem to go for slightly over 5 seconds per lap.

I hear the smallest steel lines are sometimes difficult to handle (like .008" diameter). Many fly .049 engines on fishing lines but you need to get the right choice there too, in diameter and brand. Stretchy lines are not good for control...