I’ve no access to Dennerle but either ADA or Tropica are equally good, just different
Follow the recommended protocols for either methodology for best/most consistent results
You don’t need Power Sand or Tropica GS unless tank is super high powered or you want a long term scape (greater than 1 year)
Any layering means more mess if you like to move plants about/replace or adjust hardscape
Given you’re young and likely have house moves ahead and may wish to “practise” scapes, I’d keep it simpler - and less expensive
Water column fertilizers will support and extend soil lifetime
I’ve recently replaced my older Tropica Soil and the increase in leaf growth and root growth and plant density is noticeable ... I tend to limit water column nutrients (re fish preferences) AND my tap water is extremely soft, it’s possible if you follow EI methods, aquarium soils will have a longer “high power” lifespan