>>96049850
One ritual with no time costs per dot of Thaum is the standard rule, not a house rule.

What books you're allowed to take from? Nevermind, I'll just list the common ones.
Sacred Haven, Evening Freshness, Communicate with Sire, Purge the inner Demon, Purity of Flesh, Introduction (yeah, it's useless, especially if you're stuck in a chantry for fifty years, it's still the tradition), Infusion, Sanguine Assistant, Talisman/Phylactery are all but mandatory to learn eventually. The latter specifically is the customary Tremere's fifth dot ritual, even if it's hard to perform and would successfully performed only once, you'd have to put more effort into convincing the storyteller to pick another as your fifth dot.

Mask of Shadows, Incorporeal Passage, Blood Walk and Vires Acquirit Eundo are very common. Pavis too, but only if you're trusted not to reveal it even unto death. Most players develop some sort of Willpower-refilling ritual, especially if playing with permanent Willpower at risk rule. Fiery Touch and some of the weapon/stake/projectile enchantment sets would be known by combat specialists, but rarely by someone else.

Regent generally needs to know Wards, Contract, Transubstantiation, and One Mind of the Covens. The latter three are also a must, as they are Tremere's ways to enforce control and coordination of the clan; a chantry that doesn't bind their apprentices, doesn't officiate its agreements properly and doesn't join magic zoom conferences is liable to get purged.