I suggest thoroughly mixing the clay with the manure before adding it to the hugel. Roughly a 50/50 ratio. That seems to help my heavy clay avoid turning into brick layers. I also add a few leaves & small sticks into the mixture. Consider starting with as many earthworms as possible & doing the Ruth Stout method of burying kitchen scraps to encourage worm populations to thrive. I don't bother removing soil from sod. What I do is flip it over & bury it deep in the lower levels. It seems to work but some really persistent grasses or invasive plants might need to be removed first.
Well composted horse manure seems like it might not be great for mulch. I think too many undesired plants (weeds) will grow directly in that. I think a thin layer of manure covered by a thicker layer of straw (or leaves) as mulch might work better.
It looks like you're off to a great start with this hugel!!! Try looking in the regional forums &/or your local gardening suppliers for specific suggestions on what to grow there. Good luck & welcome to permies.
Hard to tell from the pix but it looks like there's a slight slope. I built a trench to capture water on the uphill side of mine. Slowly but sure that's becoming a hugelmoat. https://permies.com/t/117821/permaculture-projects/chicken-hugel
In case you haven't found Dr. Redhawks's excellent soil series yet. https://permies.com/wiki/redhawk-soil