If 5C is whiffing, then they are typically too high. If they are above your head, 5C will typically whiff and you gotta just go into jD. If 4B[1] is hitting, then you might not be delaying 4B. After hitting with all hits of 5C, you want to slightly delay pressing 4B. If you press it as soon as you can, 4B[1] hits most of the time in my experience.
Don't worry too much about the timing of the dash. As long as you end up near the opponent and can 2C them before they tech, you are fine. I haven't found distance from the opponent to be too big of an issue. Just try to dash as soon as you can and hit with 2C as late as you can.