I would start out with 5iu, taken preworkout. Be sure that you understand how to feed carbs to the insulin before you start. A good rule of thumb is 10 carbs per 1iu. I would eat 45 min pre workout, use an intra workout carb as well as carbs post workout. After you are confident with 5iu, increase by 1iu a day, making sure that you are getting enough carbs to keep from going hypo. I'd go no higher than 10iu per shot and would use four weeks for your first cycle. Then from there, if you want to go back on for another cycle, once you have built up your preworkout shot, you may consider adding a shot at another point in the day, once again, starting at 5iu and building. I would go no higher than 8iu and then 10iu pre workout, for a total of 18iu a day.
ALWAYS keep simple carbs on hand, in case you begin going hypo and never take insulin if it is still going to be active when you go to bed or take a nap
The internet would have you believe insulin is very dangerous. And yes, it can be, but if you know what you are doing, you can use it without issues