1. Your caster level for the mythic books is equal to twice your mythic level.
2. You will always gain all the spells unique to your path.
3. You get to pick to a few extra spells that are drawn from either the wizard or cleric lists. Some do have a mix of the two. Does not seem to be goverened by any stat when it comes to spells per day / learned / which level of spell can be used etc. Didn't do much testing here though (yet).
4. Angel and Lich can merge their spellbooks. This is a choice done on mythic level up. Angel can merge with Oracle and Cleric. Lich with Wizard and Sorcerer.
5. If you merge spellbooks, you keep your normal spellbook for that class. But all unique spells are added to it when they are unlocked. Your mythic level will stack with your caster class' level for determining spells known, spells per day, etc. (10 Angel 10 Oracle = cast spells as if you were a level 20 Oracle)
6. Arcane spellbooks suffer from arcane spell failure. Divine spellbooks can cast in armor without worry. Nothing special here.
7. Angel and Lich get 9th level spells. We also know they get access to 10th level spells, if you merge spellbooks and go beyond 20 caster levels. All other paths get a selection of up to 6th level spells, with one or more unique 7th level spells on top.

Here's a breakdown of the paths:
Angel: Uses WIS, divine caster. Gets to pick spells from the full cleric/oracle spellbook?
Lich: Uses INT, arcane caster. Gets to pick spells from the full wizard/sorcerer spellbook?
Demon: Uses CHA, divine caster. Picks from a number of wizard/sorcerer spells. Lots of duplicate spells and spells that do nothing, seems very unfinished.
Aeon: Uses CHA, divine caster. Picks from a number of mostly divine spells with some arcane spells (Transformation for example) added in.
Trickster: Uses CHA, arcane caster. Gets a number of wizard/sorcerer spells, mostly focused on the illusion spells and other that fits his theme.
Azata: Uses CHA, divine caster. Gets a number of cleric/oracle spells.

(No it's not a typo, CHA really is used by all those paths)
(That Aeon, which stacks his bane ability with Inquisitor, uses a different casting stat is really strange)