Not sure about the saya's fitting, Mark would have to answer that one.
I do really like that stone set. I've come to favor the Ume 1k a bit over the 1,200 Bester....but the Bester is still a really great stone and something I still use today and have used very happily for years.
You don't "need" a stone holder, but they're nice to have......either that or a sink bridge:http://www.chefknivestogo.com/nasibr.html
I prefer the sink bridge.
You can make a sink bridge or a stone holder from some of that sticky shelf liner stuffhttp://www.amazon.com/Duck-1100731-Non- ... 049&sr=1-3
And a 2x4....but the stone holder or sink bridge is just ready made.