I use myco all the time. Pro Mix contains a starter charge and I also add more when I transplant. They are especially effective in organic mixes. I would also suggest using some humic/folic acid in your mix. It can be purchased in powered form and added to your mix, or fed as part of your nutrient regime in liquid form. It will help to break down your organic matter to better feed the fungi.
Just know that Mi5 grows great, yields well and is a great, well balanced smoke. Growing in Pro Mix I've run into some slight N deficiencies in early veg, and some P deficiencies well into flowering. But in your mix I doubt you'll run into them. I'm sure they will do great for you.