Running it now and loving it. Yes, it works as a system for Warhammer; instead of the Demon Lord you have Chaos and whatnot, though the ancestries and religions will be different.
Zero-level play is basically fantasy Call of Cthulhu, where the real goal is to survive and learn the basic rules. Characters at that stage aren't proactive and don't have much they can do yet. It's great to teach the game at the beginning of a series and show how the characters became adventurers, but for a one-shot it's probably not very interesting. Go with pregen 1st- or 2nd-level characters instead; they're still simple enough but have stuff they can do to feel useful.
Miscellaneous observations:
* The math is very flat, as much or more than D&D 5e, so expect characters to grow more laterally than vertically. It also means that superior numbers matter a lot in combat. Also, boons and banes give diminishing returns, so don't be stingy with boons or worry that you're giving too many. As for the whiff factor, note that everybody ends up with a way to apply boons to actions, and what differentiates the novice paths is the different ways they do it. 0-level characters, however, are not going to have that benefit.
* Another reason numbers matter is that the action economy is tight. It's even tighter than D&D5's. That means it's very straightforward, though I have noticed one problem: because of the name, players often assume that a triggered action must be in response to something another character does, which is incorrect. Some triggered actions are indeed reactions (free attacks, prepared actions), while others are just bonus actions that are "triggered" by whatever talent you have that lets you do the thing.
* The Demon Lord's Companion is the rest of the corebook that wouldn't fit. Everything else is optional, but the big supplements are awesome for anyone using the default setting (which I like very much). The mini supplements are also very good for the minuscule price, but be aware that the ones dealing with injury and madness make the system more complex and are not recommended for your first time.
* Forbidden Rules features some optional rules that I highly recommend, such as simplified equipment and abstracted movement/range. I think those ought to have been the default. The rest are arguable.
* The published modules are mostly good, or at least okay, though a campaign made up of nothing else will feel a bit shallow. They're good for getting you started on an arc in a particular place, however. For starters, I recommend "Dark Deeds in Last Hope" or "The Witching Wood," which manage to be interesting despite 0-level characters' lack of doodads.
* There really isn't such a thing as a "balanced party" or any particular reason why anybody should feel pressured to play a path other than interest. Outside of a one-shot, characters will end up significantly different from each other even if they all choose the same novice path. Nor is there any reason why you have to have a priest in the group. The real issue is preferred playstyle or theme for the character. Nor is optimization something players need to worry about. The game's designed to help novice players create good characters without having to plan ahead or master the system beforehand.
* It's best not to treat combat as a requisite thing that you have to do every so often just because. It comes with greater risks and costs and fewer benefits than most forms of D&D, so it makes sense for characters to avoid it when possible. On the other hand, combat is fast and painless on the mechanical side of things.
