Hm, does it make sense to multi to a cleric at level 7/8 and later merge spellbook with angel?
Or given the late caster start, is it better to get a separate mythic spellbook (and maybe skip cleric then)?
What are you trying to do with your cleric?
Well, the idea was to get angel caster levels to get Frightful Aspect, Divine Power, Righteous Might, Eaglesoul, Archons Aura and a few other buffs. Maybe a few healing and offensive spells too.
Angel should make this possible even on multiclassed character. But I wonder if it's even worth it - since it will come late AND separate spell books can offer decent spell selection too (probably no Frightful Aspect, though).
Just go full oracle with battle and life mysteries? But yeah that'll work if you only go cleric path for buffing and healing.
But I really like my Sohei...
... just don't feel it's a great investment past level 6 (or 11).
I made a couple of versions of my build, just to see what was possible. It was made for soloing the game though, not for playing with a group. Here was the armored version, it had no dips at all, although it could benefit from 2 paladin levels (mostly for smite evil).
I didn't go life domain, mainly because it feels really unnecessary considering the angel healing spells. Its battle domain and ice domain, taking seamantle and ice body from ice domain, as well as some of the feats. Take note that even though spells like magical vestment state they stop giving additional bonuses above CL 20, they actually do keep giving bonuses above CL 20. I did also theorycraft an unarmoured version, which benefits far more from ice domain, since it gets to benefit from ice armour. This one is more "dip heavy" and probably is more in line with what you are looking for.
All in all though, I just don't really feel like multiclassing a divine caster is worth it. Sure you can maybe eke out a little bit more power from it, but not much.