Thanks for your feedback!
@1: In order to kill the villagers you need to first poison their water and food supplies. Each village has one water and one food supply. Then, the villagers who live there will be infected. (You can always see the number of infected villagers in the top right corner.) Using your ultimate ability, you can then kill the infected (not the healthy ones). Your ultimate ability takes some time to cast - so make sure that you are in an area where no farmers will discover you. They discover you when you are casting, and are in a certain (quite short) range of your character.
@2: Whoops, thanks, that's a bug. Obviously I only tested it using WASD ;-)
@3: Yeah, thanks for the input, maybe I'll redesign the dialogue boxes in a future version to be on the bottom of the screen (or somewhere else, where they are not in the way).