No. And little bit "Yes."
The Life 5 Rote Perfect Metamorphosis, and its associated sphere trait, allows you to make a perfect modification of the living, physical form. It would, for instance, allow the Mage to turn himself into a human/wolf hybrid similar in physical appearance to any of the five forms, such as Crinos, and even shifting between them. It might also allow a Mage to turn himself into a human-esque being that feeds on blood (using a vampire bat as a model) although this would likely require far more than a typical Kindred. However, every known multi-cellular organism I am aware of requires some form of respiration to live, though for most plants this is usually carbon-dioxide instead of oxygen; and there are thriving ecosystems near volcanic vents which survive based primarily on sulfur and methane.
While this could, theoretically, allow the Mage to mimic most of the life (or unlife) functions of another creature for a period of time, evading most methods of physical identification - prolonged usage would almost guarantee discovery. How long this would take would likely depend on your GMs suspension of disbelief for scientific plausibility. Almost all forms of life require some form of respiration and non-lung methods break down at large sizes. The longest times recorded for mammals holding their breath is between 90 and 120 minutes. Almost all multi-cellular animals have some form of circulatory system and most have a heart. A vivisection (ouch!) would immediately reveal most of the methods used to evade detection.
Additionally, in the same way as physical evidence there is the issue of magical evidence. While you can mimic most of the physical effects of being a shifted Garou or a Kindred and even some of the supernatural abilities with Perfect Metamorphosis, most of their abilities lie outside this Sphere. Garou, in particular, make use of their spiritual abilities rather frequently. And let's not forget cultural evidence. A Kindred or Garou who doesn't know the traditions of her people can get into a very large amount of trouble very easily. Even being a new member of the group is not always a suitable excuse and that would assume the Mage knows enough to fake even that. After all, new people at Elysium or Moots are usually spotted rather quickly.
This form of hiding is almost entirely vulnerable to magical means of detection meant to identify specific types or classes of creatures. Again, GM determination on whether your form falls within the range of a particular supernatural detection ability. A Life 1 spell meant to detect non-humans would almost certainly hit you. A Life 1 Matter 1 spell meant to detect Vampires would likely not. Whether Sense Wyrm could differentiate you from a true Kindred is open to cosmological debate as to what, precisely, about Kindred it is that this Gift detects.
Regardless, within the World of Darkness canon many of the supernatural abilities inherent to either Garou or Kindred are not solely the result of biology. Notably, Werewolves have significant spiritual investments from Gaia that allow for things like stepping sideways, the delirium, and Gnosis. Likewise, all Kindred but the Thin-Bloods are repeatedly written in terms that indicate that they are reanimated corpses solely sustained by a combination of the Curse of Kain and the blood of others. Disciplines, basic stat boosts, and other forms of blood conversions, even healing, are also another matter as it is the Curse itself that allows this transformation.
You may be able to skirt some of the issues with Kindred without the use of other Spheres by becoming a Ghoul (at the GMs discretion, of course). However, this has some serious drawbacks including addiction and the Blood Bond.
Any physical interactions with Kindred require use of Life and Matter due to the Quintessence-infused blood sustaining the animate corpse1 and Garou require use of Life and Spirit due to their half-spirit nature2. Outside of this, how the Mage cosmology interacts with the Werewolf and Vampire cosmologies is an exercise largely left to your GM. There are intentionally a great many places where at least two of the three cosmologies line up and their interplay can lead to some fascinating campaign ideas.
Overall, its probably best to keep in mind that one of the whole points of the way the Mage: the Ascension magic system is written is to allow inventive solutions to problems. Often, things that can be handled with one sphere can be handled via a different interpretation with another. In Mage, Paradox is pretty much a high level Mage's only obstacle to Total World DominationTM. However, one rule of World of Darkness has always been immutable. You may never have two templates at once, and the Tremere are a perfect example of what happens when you try.
1Mage: the Ascension Revised Edition (WW4600); page 280, Notes: section of Young Fangbanger.
2Mage: the Ascension Revised Edition (WW4600); page 282, Notes: section of Hot-Blooded Warrior.
Keep him protected by building enough power among your kind that they will respect your claim on this person. You need to make some political allies among your fellow Kindred, pronto. Many Camarilla Kindred maintain mortal contacts that they want to keep protected. A chief tool for this is "if you mess with this mortal, you are messing with me; and, by extension, anyone in this city I have some sway with." There is often a gentleman's agreement stay away from a human another vampire claims, because it ensures that vampire stays away from your humans. This, however, still presents you with a problem if you are a relatively weak vampire (in the blood and/or politically) claiming a high-value mortal.
It's going to be an uphill battle to hold on to your mortal. You'll need to invest a significant amount of your energy and political strategies towards this goal.
- Find ways you can perform boons for Kindred that can help keep the mortal safe. Ideally some, but not all, of these vampires should be ones who might otherwise try to mess with your mortal.
- Gain gossip and blackmail material where possible.
- If you only care about the mortal on a personal level, and not for his temporal power, you try to lower his profile. Other vampires will care less about him.
- If you want him to keep his power, gently use it. You are investing your energy into this man, and if you don't get some return on that it's unlikely that you can maintain enough power to meet your goals.
- Don't piss anyone off too egregiously! An angry vampire will hurt your mortal to be vindictive to you push things too far.
- Don't spread yourself too thin. This mortal represents a risk. Do you claim a small neighborhood as hunting ground? Have a Herd elsewhere? Other people or places you want to protect? Each addition thing/person is a liability, and a drain on your ability to keep them safe.
- Bluff when it makes sense, and don't when it doesn't. Some of Vampire politics involves a shell game.
- Try not to let on how this person is important to you, if it's personal. If it's too obvious he will be used threatened and used against you by an opportunist. A mortal you claim for "business" such as food or temporal power is normal. A mortal you care for as a lover or kin is a big risk because people know you might do anything for the person.
All of these approaches are things I've done or seen done in actual games.
Good luck, you've got a problem that can make for an excellent plot line!
Best Answer
Like many things, it depends. Your calculations are quite reasonable and 372 should give your vampire enough, in fact it has a decent margin of error in it. It has a decent margin of error because a healthy person can give more than 1 BP in a night. I don't have the book handy, but I'm pretty sure they can give up to 3 BP before their life is endangered. Also a healthy person can give blood more often than the medical guidelines indicate. Further, the vampire can, at least to a degree, self regulate and avoid using unnecessary blood. You will still average well above 1BP a night, but a vampire that avoids fights and is deliberately conservative about blood use can probably come in under 2-3 BP a night on average.
So, as you say 372 will provide enough, and even give some safety margin. But that is 372 adults that are at least healthy enough to "contribute" three times a year. You are asking how many would be in a community to give you those 372 healthy adults.
And that depends. You want the birth rate to be equal to or greater than the death rate, but death rates are highly variable in different time periods and different parts of the world depending on circumstances. In the United States, for instances the crude death rate is 8 per 1,000 people per year. Going with that number and ignoring the fact that that is per 1,000 in the entire population and we are only looking at health adults in our 372, he can expect to lose around 3 of his herd each year. That means to be sustainable he needs 3 that are about to become old enough waiting in the wings. If we say they are "adult enough" at 16 and we want this to be indefinite we need 3 children at each age between newborn and 15 waiting around. So, in addition to our 372 adults, we need 48 children waiting around.
Incidentally, the crude birth rate in the US is 14 per 1000 people, so for our 372 adults we could expect an average birth rate (if comparable to US) of 5, easily more than the 3 we need.
Currently, this brings us to 420 to be sustainable. But, you also won't be able to count those with chronic infirmities that prevent them from contributing, like the very elderly. But how many elderly you have also depends. If the death rate is high, you probably won't have many. If you have customs of senicide (killing or suicide of the elders), then again you won't have many. If the vampire has a firm hold and wants to keep the population to a minimum, he might well create such a custom or else "cull" his herd of any not of use to him. If he does this ruthlessly, than 420 is enough with a decent safety margin. But, if he doesn't do this then he will have some additional people. In the US our population over 65 is 13% of total. With a base of 420 people, this makes 483 people total (13% of 483 is 63), so if this is a rough estimate of the number in his population he can't eat than we are up to 483.
I'm ignoring the temporarily sick because (unless there is an epidemic hitting a large percentage of the population) he can easily bypass them for a week and just come back. In short, they are absorbed into the safety margin.
So, I've played rather loose with a lot of the estimates and erred on the side of the vampire being cautious, but a population of 483 could sustain a vampire forever. This of course adds in the assumption that there won't be any huge deviations from average. If there is a war or plague or famine that wipes out a large portion of the population, he will have trouble.