Developing times are highly personal and should be optimized for your workflow and the paper you print on.
"Normal" development, i.e., development for scenes of "average" brightness range (contrast), should yield an "acceptable" print without much manipulation for such scenes on the grade of paper you consider "normal." For most workers, this is grade 2. Some smaller film-format users prefer grade 3 in order to minimize grain a bit. If your negatives from normal scenes are consistently too contrasty to print easily on your normal paper grade, reduce developing time. If they are consistently too soft, increase development. Keep adjusting till you are happy.
Since you are a roll-film user, I would recommend that you just leave it there and use your paper grades to deal with scenes of higher and lower subject brightness range than normal. If you want to tailor development more specifically to your individual subjects, then learn about one of the exposure and development systems like the Zone System or BTZS.
As for a starting development time: I would recommend that you try the development time that the film manufacturer recommends. I doubt that Kodak gives different development times for shooting the film at an E.I. of 400 and an E.I. of 200. If you are using a developer that Kodak does not give times for, use the times the developer manufacturer gives for Tri-X 400. Adjust from there.