Sounds like you have a great start. But that's probably the easy part. What has me puzzled is how to make designs. Cantle makers showed some creativity in this. Sometimes they drilled holes and then filled them with brass bits we may no longer have to leave reverse dimples. I can see how to do that if I can find the bits (upholstery tacks?)

Sometimes there are concentric circles, which shouldn't be hard to mill out with a drill press and the right jig. What I think would be ideal would be a reverse pantograph where you could move a template around a large circle but it would come out as small, precise circles at the business end. or...

Something I've not seen done in brass, but that might be nice, is cutting out designs so that they show up behind the brass in a felt underlayer. Or use silver sheet behind the brass, or copper. I've always liked silver, brass, copper layers, but prefer the copper on top as it tarnishes fastest.