Buffing is not a good way to remove scratches. Hand sand (or use stones) until no more scratches, then go to the next finer grit in a different direction until you're happy with the scratches.
Since you're etching for a pattern you probably don't need to go finer than 400 grit.
The most common etchant is fairly dilute ferric chloride (a.k.a. Radio Shack PC board etchant). Vinegar, especially hot vinegar is also used by a lot of makers. It's slower than ferric, but
that's actually an advantage. One problem you're having with the muratic is that it's too fast so it etches all of steel too evenly.