Plan for this winter?

[OneDahlia]

I have a new garden bed in Virginia clay soil, and I want to amend it as much as possible this winter. If I layer horse manure/wood shavings/a little straw, plus grass clippings (no chemicals), leaves and coffee grounds right on the bed, it will decompose enough by spring, right? Do I have to shred the leaves? Should I turn it in with a pitchfork as I add it or just leave it alone until spring? And when should I stop adding stuff to give it enough time to decompose?

Also, I'm assuming that amendments like this and cover crops are an either/or situation, right? I wouldn't do both? Or maybe I should grow a cover crop, compost all the other stuff, and use it in the spring? But then I won't be able to apply as much of the amendments because I don't have a very big space to compost.

Is there anything else you would recommend adding? I haven't had a soil test -- figured I'd do that in the spring after all this stuff is part of the mix.

(Sorry if these are really basic questions!)

ETA: I just found a thread on horse manure. Hmm. Lot of varying suggestions there. I'm getting this from a friend who normally spreads it back over her pasture. Hoping that means it's OK for the plants. Last thing I want to do is cause new problems.