My first word of advice is, don't over-think your soil. You don't need to come up with complex soil mixes that contain 10 different ingredients and several you can't find anywhere. You want your soil to be loose, airy, and free-draining, but still capable of retaining some moisture. You can achieve this with a multitude of different substrates, and no soil mix is the 'correct' one. A couple of my favorite products to use as additives are coir (coconut peat or 'Beats Peat' as it is marketed where I live) and Turface or aquatic plant soil, which are both sort of a fired clay granule.
Planting is best done in the fall. I have planted Cyps in the summer, even when they were in bloom, and never had any major problems that I can recall, but I still prefer to plant in fall and these days when I buy plants in spring or summer I like to sink the pot in the ground to keep the roots cool over summer and plant in fall. Spread the roots out horizontally in the top 4 inches of the soil, and make sure the dormant eyes are about 1/2" below the soil surface. Plant too deep and they rot or at the very least fail to bloom, too shallow and they can freeze or rot over winter. Make sure you don't compact the soil when you cover the rhizomes, I like to sprinkle it lightly over top. Then I cover with a 2" layer of mulch, which I pull away in the spring. That's about it.
In my experience kentuckiense is somewhat prone to rot. Many recommend using sand in the soil mix for this species. I have grown it both with sand and without and have had success and failure in a variety of different mixes.
Good luck!
