You know next to nothing of Sakura's situation in the VN at all until HF. You know that the grail is corrupted in all three routes, but only in HF does the issue directly involve Angra Mainyu rather than just a big abomination of black goo. You get a little insight in Fate by Kirei, but it's not much. Kirei only goes off on his monologue about Mainyu during his final confrontation with Shirou in HF. This is the stuff that Urobuchi went off of to write the core plot of F/Z.
You also don't really learn much about Kiritsugu's involvement until Kirei mentions it in HF. You actually don't get much anything even there; Urobuchi took liberties with that and made up his abilities for the story. They are canon now.