Seems like I spoke too soon about the display and keys.

Jelly-bean 6x6mm keys do have quite big footprint and I can place four of them into width of 55mm, which was my personal limit of width. Display is quite big as well, so I have to make the board 57mm wide.

Well, I'm going to think about the dimensions and components again; I have to maek decision whether to use common components or keep the physical dimesnions small.

By the way, I set up github repo for this project and I'm uploading there work as it progresses.