There would be crossovers between Mystics and Stormcrows thematically, but it’s the focus in game that is subtle but becomes very obviously different through play. The short version of it is that Mystics are magically based and Stormcrows and Religious (Virtue, particularly religious birds) based. Both give advice, but the manner would be different. A Stormcrow might tell a poetic story of a great Hero’s Heroism and Virtue to inspire another, or how they measure up to the great hero, a Mystic will trace a line of Runes to determine anothers Skein.
With Mystics, there are various methods you can use to do divinination, 1 is the Hard RP method and it’s a tool to create RP opportunity (TBH a lot the time people just need encouragement to do the thing they already want to do), Have a look divination for that. There is also magical Rituals if you want to do bigger things, but also Herbs (which is a big thing), Infusions of Feathers came from Kallavesa and is quite iconic look of that raggedy Mystic with smoke and teas.
I am a little puzzled though, you wouldn’t be “Half Kallevesi half Steinr”, it doesn’t work that way, you’re either one or the other. Being a Kallevesi in Hahnmark is perfect and entirely normal, just because you’re from Hahnmark doesn’t make you a Steinr. If you mean parentally determined, that doesn’t happen, you choose what tradition you belong to when you become an adult. It sounds like from what you’re wanting you are a Kallevesi in Hahnmark, using runes and the like is totally on brief for a Kallevesi and big and clever. The look and the characterisation are different, the look and behaviour you’re describing is certainly someone who is a Kallevesi.
Direct answers/TL:DR below:
Does this all seem reasonable/heretical?
The half Steinr/Kallevesi seems off as above but yes that seems fine. Bear in mind most the religious briefs could be perceived as Heretical in game and is a feature not a bug (The big dirty bird worshippers we are )
Would it be odd/normal for a Crow to read runes?
Entirely normal yes, I do it. It’s Hearth magic so runes are part of our lives.
What would your IC reaction be to this?
Yup they’re Kallevesi, which rune is the day marked by?
What would a Crow say that a shaman wouldn’t?
It’s more that Crows talk about VIRTUE BIRDS, GREAT HEROES, divination and skein and Mystics talk about DIVINATION, SKEIN virtue birds and great heroes. A Mystic would be perfectly at home in the Sevenfold path. A Stormcrow would do Confession where a person talks about lapses in Heroism and virtue and fraying of Skeins and a Mystic wouldn’t do the confession in regards to Virtue. One can totally see a Mystic and Stormcrow working closely together as a team.