1. As DeathStar said, few recipies have a 100%, although I've heard some do, skeleton steel sword isn't one of them.
2. Whether you use primary or junior, it's a +3 compound, so it will be a little rare, getting your alch lvl higher may help with that, or you can use an alchemy book.
3. Skeleton Steel Sword is base: Steel/Canine, and there are no other items that have that base. So it's either you make it or you fail, meaning this compound has a high chance to fail.