I couldn't find anywhere in the docs (did I miss something?) a way to change and save the roster dimensions; everytime after I run Tkabber, I must then manually set more comfortable size.
Does there exist a way to make the new size setting permanent?
Right now only manually
This is a feature I want myself, since right now Tkabber does not store almost any user interface data: roster width, chatrooms roster width, windows sizes, windows positions... Any of those changes are stored by Tkabber and retrieved on next run.
One solution: you can manually specify all this variables in a .xrdb file or in your personal config.tcl, like I did. Take a look at my example files badlop-dark.xrdb and badlop-config.tcl. You are interested in the variables called 'geometry'. You can make some experiments with them, include them in your personal config.tcl, modify them until you are happy with the results.
Of course, I would prefer that those variables are stored directly by Tkabber when you move the window, change its size, change the roster width, etc.