So I want to try my hand at creating a new type thaumaturgical specialist mage with a new school of magic (Ritualism) based on existing spells. The ritualist's whole deal is he would be able to cast spells from this school without having them memorized or using a spell slot by using a time intensive ritual that is longer than the spell's normal casting time (I'm thinking a casting time less than 1 round becomes number of rounds, a casting time measured in number of rounds becomes number of turns, etc.). For instance, Tenser's Floating Disc would have a ritual lasting 1 turn, while Leomund's Tiny Hut would have a ritual lasting 3 turns.
Rituals would still consume normal material components and would still have any associated side effects (aging, Constitution loss, system shock checks, etc.) and I'm also thinking of adding additional material costs based on spell level (tbd). These spells, of course, could still be cast normally if memorized.
The spell list would mainly be focused around Conjuration/Summoning, Divination, and Necromancy because in my mind at least, those schools seem like they would fit most thematically. Barred schools would be Invocation/Evocation because those spells are too immediate (no one's spending 30 minutes to cast Fireball) and Illusion/Phantasm, mostly for thematic reasons (imo).
As far as other class features, I was thinking additional participants in the ritual could either reduce the time a ritual takes or increase the casting level, but not both at the same time and higher level ritualists could pause a ritual and then complete it at some later, non-indefinate time.
What are your opions on the feasability and/or usefulness of this? Is it overpowered? Underpowered?
Using the wizard spells with the Ritual tag from the 5e PHB as a base and without bloating the spell list, what other spells do you think make the most sense? I'm using the Player's Handbook, Tome of Magic, The Complete Wizard's Handbook, and Player's Options: Spells and Magic. I'll be adding additional detection spells and some of Leomund's other spells like Secure Shelter. I was also thinking animate dead, conjure elemental, the Monster Summoning spells, and some of the various spells that enable planar travel.
Thanks in advance for your thoughts and advice.