[RPG] How to avoid letting the players keep too many ghouls

By canon, any metro area can support 1 vampire per 100,000 mortals. This is the only population limitation in the old world of darkness. That said, vampires are supposed to be the most common supernatural creature (excluding the allies; ghouls, kinfolk, etc. which are just mortals).

For example, the Edinburgh metropolitan area has a population of about 780,000, which means it can support 7-8 kindred, which means there will be less than 7 Mages, Werewolves, and setting permitting, Changelings. As a Kindred can typically support at most 4 ghouls, there are likely no more than 32 ghouls. Many of the other splats would be unknowable.

It should also be pointed out that the 1:100,000 ratio is an in-character artificial limitation; Page 29 of Revised Edition VtM states:

A rough ratio of vampires to mortals has evolved in the last century. Many vampire princes enforce a limit of one vampire per 100,000 mortals, in the interests of keeping the existence of the Kindred a secret. Nonetheless -and particularly in the last few years -some cities exceed this ratio, and the ever-growing population of Kindred is becoming a very dire concern. In cities that do not slavishly heed the Masquerade, such as those under Sabbat control, the ratio may soar to two or three times the acceptable level. Overpopulation is not an easy problem to address; arbitrarily deciding which vampires may stay and which must suffer the Final Death is a matter of policy no prince wishes to decide, except in the most critical of circumstances.

I'm running a game that blends VtM V20 and 2ed. In that game I have a few considerations:

For player characters I think that it should mostly be dictated by roleplaying experience more than age. If they want new rituals, it becomes a matter of finding the resources and then enough game time passing. We usually treat this sort of thing as an extended roll. For my group, this exact scenario hasn't come up because we don't have any serious magic users.

For NPCs I have two tracks. For NPCs in the city's "milieu" (which means they exist for the players to interact with but aren't major agents in the plot without player intervention) I mostly build the character according to the standard character creation rules and then give one ritual per dot in any magical path (not discipline) of equal or lesser level than the character's overall corresponding Discipline rating.

For major NPCs (those that drive the plot with or without player intervention) it's pure storyteller need. The rituals themselves are really not balanced well within or between sorcerous Disciplines, so I don't like limiting such important characters while creating them-- the builds end up too fragile to deal with players taking the story off the rails, and useless rituals are a waste. I do try to stick to the one-ritual-per-magic-path-dot, as with milieu characters, but I don't assign all of the specific rituals right away.

I'll give major characters rituals that the character "would know", in the sense that if the character regularly does something a ritual supports or makes possible, then the character knows it and this "uses up" one of the allotted rituals. The rest are fluid until they are needed. This flexibility remains until the chapter in which the players first meet the character ends (more or less), and then the rest of the fluid rituals are assigned to ones I think fit their concepts and backstories or they are lost. For high-level rituals I might require the NPC to devote resources to discovering/learning them "off camera", but that ties in with some other house systems I use.

TL;DR: The rituals an NPC knows (and their number) should support the needs of the story first and foremost regardless of any guideline. After that I aim roughly for one ritual per path dot, loosely adjusted for the NPC's access to ritual knowledge, inclination to study, and relevant Attributes, Abilities (primarily Intelligence and Occult, but others sometimes apply), and Disciplines.