Have you -at least- ever designed or built either a low power class-D amplifier or SMPS? If not, I would suggest that you do it first, and get your feet wet on the devilish details of those circuits.
In particular, the design of the magnetic components for the SMPS at those high power values is a science on itself. Also, heat removal, board layout, closed loop stability, circuit protection...those take lots of experience to properly master.
I am not attempting to discourage you. All I'm saying is that you need to learn to crawl, then to walk, before you can run.