I, surprisingly, actually have some suggestions to help you out Flabort.

I like the suicide zombie bit, but make it a random zombie, and no one is told, not even the zombie. The only way to tell is by a scry, or being lynched and then exploding a lyncher. I would take out the ability to suicide on purpose though, seems counter productive to the horror bit.

Make the recruits secret. If your going for a zombie thing, the one thing scarier than a zombie is the thought that your friend might be bit. They won't actually change till a few days later, but are informed that they are bit. They have the option of helping the zombies, because they will turn into them eventually, or informing the survivors and dying the next day.

Another thing, put some more guess work. Each recruit, when fully infected, has a one in ten, or what ever percent give it an actual chance of happening but rare-ish, chance of being a suicide zombie as well, but aren't told.

Make a few more roles for the zombies to give the wizard some more utility. Perhaps a zombie that can reduce votes during the day against a certain zombie? Not total immunity, but more like blocks about three to five votes against said zombie. Perhaps it can be a random roll on a D6 for effectiveness? A set number can work as well however. I would make this power usable during the day, or night though. In private though, revealing either nothing, or that a zombie was seen acting protectively towards another oddly, no names given.

Now... A problem would be a bodyguard giving up other bodyguards when changed. I don't really have much of a suggestion here, unfortunately. Well, I do have one but it is much more trouble than it's worth. The suggestion would be to have them pass notes to each other, unsigned in name. To prevent them from just telling each others names also, perhaps give the notes a chance of being discovered. Once again though, I don't think this is actually a good idea however.