You can't really go wrong taking it pre workout at any dose. In my experience and many others the more the better. However for most 2-3ml is plenty. You should get great results at that dose. I would recommend starting at 1ml the first day then 2ml the 2nd day. 2ml may be enough for you and I know many who stay at that dose. I can definitely feel the difference when I up to 3ml and of course even more. Most of the times when I am using it I just dose it at 3ml pre workout.
For guys who want to dose higher you could go about it in 2 ways. Many (especially competitors) do morning cardio and training in the evening. In that event I would dose synthetine at 2-3ml twice daily before each session. I have done this in the past with fantastic results. Guys could also just dose it very high once daily if they don't want to inject twice.
Insulin is beneficial when dosed with synthetine but is not needed at all. Although as little as 2-3iu slin will help transport it into muscle cells. My ultimate protocol would be 2-3iu slin with synthetine pre fasted cardio. Then approx 5-10iu (depending on goals/diet) of slin with synthetine pre weight training with an intra shake (EAA's, peptopro, hbcd's, citrulline malate, beta alanine, taurine, creatine etc). For guys wanting to gain size even long acting slin could be used with synthetine (and gh boosters) to help stay relatively lean whilst you grow.
You can get technical with it but as long as you dose it pre workout at any dose you will be gtg. Good luck with your contest.