I saw your post about Ryu Hayabusa earlier. Yeah, his games are pretty well known for their difficulty, even dating back to the NES. If you haven't already done so, I would recommend trying out Ninja Gaiden II as well. A bit less difficult than the first one, but it's about the same deal.
Really interesting character we have. A lot of moveset potential lies in his usage of Ninpo and techniques found in the later games, aside from the usual attacks he does in the originals. Perhaps even a wall jump, cling and climb could work. At least this area for the most part is covered.
The music itself will be a treat too. Overdrive, Unbreakable Determination, even Iron and Sword are favorites of mine. Then the bosses can at least get in as spirits, if not stage hazards of some sort. Finally, Hayabusa Village easily works as a home stage, probably the most talked about one.
Sorry for the long post, but it feels good to have another supporter on our side. Ryu doesn't get too much talk from what I've seen, although somewhat understandable.