1) Don't layer soils - root growth won't follow your layering strategy, and the different layers can create hydration issues when you water. (Except for top dresses, which don't count.)
2) A lot of people use starter plugs like Root Riots (
here) with heavy soils. There was a good recent discussion (
here) with tips for germinating in hot soils. (Just don't use
cheap coco starter plugs with a peat-based soil )