This is what I came here to say. It finally makes sense that a circle would just randomly appear for Saber to be summoned through. It was always there. Saber has both a connection to the circle (since I suppose Saber is actually doing inscribing it), the place, and with Iris powering/utilizing it, it should have considerable strength to last the ten years it takes for Shirou to take advantage of it.
The Gil/Kirei conversations are interesting though. We can see that Gilgamesh isn't twisting Kirei into the person he became, he is merely helping Kirei past the barriers he placed upon himself. Kirei couldn't find joy because his source of joy has always been the suffering of others, he simply denied them because he was trying to be a good member of the Church. I guess it wasn't the Grail that corrupted him as he stated in FSN. It was this war that made him finally realize the truth. The Grail is just his means to achieve that level of "entertainment."
Those are Kariya's command seals, no? Are we meant to think that Tokiomi killed him?