Hi Mark,
this is really good to see.

I like how you've taken the essential design and begun to render it as a sukashi design. Doing decent drawings is, of course, the first step to achieving better results.
A few comments if I may;
I'd have a look at the horses mane again and consider trying to create more "pattern" It doesn't have to be absolutely regular but a sense of rhythm is always attractive and adds a feeling of movement.
The tail is potentially a major design feature but as it is it's sort of cramped in there and has lost any really expressive shape.
The rear legs look a bit like a man wearing a pantomime horse costume

and you really don't need both rear hooves on the rim like that, it makes the horse look too static imo.
As a general point, always consider the negative shapes. Try to ensure they are pleasing and interesting also. The design is not just the solid metal that makes up the horse. The empty spaces that define it are just as important.
Hope that isn't too much to think about....but I wouldn't have said so much if I didn't see some great potential there.
best,
fh
another idea. Try just working of a drawing, in this sukashi style, but with no seppa dai or rim. Get the horse looking convincing first and only then begin to see how you can get it to work within the limits of a circular tsuba.
Use a rough circle to work within but don't let it cramp you too much.