I'm going to try to put all my non-magic characters on mounts; predominantly horses, but I'll also try to make Byleth a Wyvern Rider.
Seeing as screenshots seem to suggest that magic is locked to magic-using classes, I'll probably have to leave my magic users on foot; as we haven't got any form of confirmation of mounted magic users, even in the advanced classes. There might be some in the final tier, but I feel that'd be a bit late in the game to make such classes available, especially since until then your magic users won't have much use for the riding skill you'd have to train them in. Best option we'd have for Magic-Knights at this point are magic-based weapons like the Bolt Axe / Wind Sword, but we don't have much of a confirmation on those either.
EDIT: In the interest of staying on topic, I'm going to go a bit more in detail about my choices in class / weapon.
Byleth and Claude will get flying training, with Byleth getting a focus on swords, and Claude on bows (basically, playing to their strengths / unique weapons).
Lorenz and Leonie will be Cavaliers with a lance focus, Hilda and Raphael Cavaliers with an axe focus, and Ignace can be a Cavalier with bows.
Marianne and Lysithea will be a Priest and Mage respectively.
I'll also try to nab Ingrid and Ashe from the Blue Lions; Ingrid can be a sword-focused Pegasus Knight, and Ashe... well, I'm not sure what I'll make him yet (as I've got two of every weapon on my squad at this point) but he will also probably be on a horse.
In the event that my choices lead to characters unlocking their hidden talents, I'll go with that, but otherwise I won't go out of my way to unlock those.