I'm definitely planning on implementing a full and optimized keyboard layout sometime during Early Access. I also prefer to play all other roguelikes with pure keyboard controls. My plan is just to force myself to play with only the keyboard for a month or so and just keep working on it until it feels fluid and natural.
Controls in general I think need a lot of work to add all sorts of little options to speed up and optimize play in general and it never hurts to have more options that the player can toggle or configure or else just ignore.
I think the character screen, inventory and talents will likely be the biggest challenge just to get something that works nicely, looks good, and doesn't detract from players that are just using the mouse. Probably the letter prefixes like your suggesting but with the option to disable them for people using mouse that don't want their char screen cluttered up with letters.