[Edi]

There is no spell research, but there is resource accumulation. Since the AAR is going to display them fairly soon in any case (barring a savegame break), let us use Necromancer as an example:

Necromantic rituals are as follows:
- Raise Dead (no resource cost, incurs 6 points of insanity)
- Minor Summoning (20 Hands of Glory)
- Major Summoning (80 hands)
- Summon Legion (200 hands, requires Battlefield)
- Transfrom into a Vampire (125 hands, requires Old Castle)
- Ritual of Necromantic Mastery (50 for apprentice, becomes Necromancer)
- Ritual of Necromantic Mastery (150 for Necromancer, becomes Grand Necromancer)
- Transform into a Lich (250 hands, requires Temple or Ancient Temple, must be Grand Necromancer)

The major summonings from Necromancy can provide some pretty seriously powerful creatures and once you mass enough of those and preferably turn yourself into a lich, you could take it down, but expect serious losses.

As far as spell gain, all mage classes have a ritual of mastery, which upgrades the starting mage into a better mage and gives them access to tier 3 spells. You gain two spells that way. The rest you have to learn at libraries or from scrolls. Or if you can blow more resources on rituals of mastery rather than summons, you can gain more level 3 spells.

Then again, many of the more powerful rituals will summon level 3 casters for you, gaining you more mages/SCs that you can use simultaneously for the same price as gaining one more spell for a mage who can only use one at a time.

As far as rituals are concerned, they are hardwired into the commanders. If you have a certain commander, say Necromancer, that commander can cast all of the rituals available to him given the resources. And if a commander can cast a ritual that requires some specific resource, he can also gather it. So if you charmed a necromancer, you could gather Hands of Glory after that, even if you couldn't normally.