The control scheme we're using, as well as many other interface navigation patterns, are already very similar if not directly borrowed from Ren'Py's handling for the sake of uniformity and player ease of use. So while we may add the option to setup custom controls in the future (Godot offers easy ways to do that internally), it's not a priority for us at the moment.
We are continuing to implement new sprites as they get made, bit by bit, and yes, currently most of the work is going into making custom expressions for Garreth and Brym as well as Yarin's side portraits.