I don't think it should be random at all. I think that perhaps it would be best just to ask us each what our habits are and then decide on the dangers based on how relatively dangerous our habits actually are with herd and what ever else you think modifying that danger of getting caught upward or downward off of that.
I think the only real feedings that should be played out, for the sake of not bogging down the game, are ones after you have used up a bit of blood for something beyond the everyday.
Here is an example of what I suggest:
Vych feeds 3 times a week taking 2 or 3 bloodpoints each time. This isn't too dangerous for her as she has a her she can feed from, and she never takes enough to leave the vessel in need of hospitalization, or serious problems, so there aren't any reports being filed for the cops or ddoctors to notice.
Sabrina is a nibbler, she like how feeding makes her feel, so she does it as often as she can fit more, generally speaking, when Jemal and Nathan allow. She tends to feed a little bit each night, never really taking enough for people to notice. its a tad more dangerous for her because of the frequency of her feeding, but with her brother supervising and altering memories just a touch here and a touch there its just her being really friendly and giving out lots of hugs.
Nikolai on the other hand may feed less frequently, not wanting to devote time to it. He may feed only once a week, but taking enough to leave the person in the hospital. He wouldn't be hunting very often, so less danger there, but because he takes soo much from the victim they end up on reports much more often raising the danger immensely.
Once you know their pattern, and you know how much they start with, all you need to know is how many days pass between the scenes. This makes feeding more about personality then utterly random. It gives pc's control of their habits, a good thing as habits are what make us individuals. I mean, we are all trying to avoid a frenzy, doing it with random rolls could have us start with 1s, something no vamp would ever ever have without having some major goings on and expenditures like spending 6 blood in 1 scene.