There's a bit of endura in-date still floating about, and it keeps well so even a few years out of date, it will still be fine. Get what you can now, if you want Endura. I am sitting on about 3000 sheets of it in various sizes, and using the oldest stuff first.
I use the 10L RA/RT kits from Kodak. As mentioned they come 4 to a case, which is a good way to buy it since it cuts down on excess shipping costs, and keeps fairly well in sealed containers, I think.