Long time dwarf player here. First off, awesome to see some new stunty happenings. Secondly, for the lore its all pretty sound from my understanding. The main thing I would suggest would be to not separate them from shield dwarves as a subrace, which I think is where you may be going. Hill dwarves were a subrace in 2ed but in 3ed the two main subraces were either shield dwarves or gold dwarves. Then from these there were more or less two types of dwarves, the wanderers (basically the adventurering types who seek out new opportunities on the surface) and the isolationists (those who just lived in their clan holds labouring away i.e. most dwarves in the world). Your clan sounds like a clan of shield dwarf wanderers, which like mentioned would be tending to venerate Marthammor Duin. It's a worthy choice mind as it gives reason why they would find themselves reaching Amia. Nothing wrong with them seeking out non-traditional crafts, dwarfs are industrious people who can (slowly) adapt to new ways. These types of wanderers are much more common in the current setting since the Thunder Blessing, due to mountain holds becoming over crowded leading to more interaction with the surface world. As for personal clan bonds, that is the norm for all dwarves in deep holds or not. For dwarves clan always comes first, as the primary organisational structure of dwarven society. So they probably wouldn't be seen as overtly selfish by other dwarves.
As for a few ideas, I am not sure if you have looked into dwarven
Battleragers who could emulate a dwarven barbarian/bard type. They tend to live outside of traditional dwarven holds as most cannot tolerate their unorthodox and chaotic behaviour for long. But they do band together in clans such as the well-known
Gutbusters. A clan of battleragers could roam the surface of the north, as mercenaries selling their sevices to human settlements and traders to protect them from orc and giant raids.
Or being from the north as you metioned Mithral Hall, they sound like they may follow a nomadic lifestyle, hunting in the long cold winters and farming in the warmer months. Or caravanning trading dwarves carrying goods from Mithral Hall to sell in the surrounding surface settlements.
Lastly, I hope you seek out Barak Runedar. There are plenty of odd ball dwarves there to rp dwarf stuff with.