Thus far I haven't managed to implement mojo's tips;I was busy with something else.
1 The video resolution issue: Still no change, tried kernel options but no luck
2 Tweaking JWM: Success! After some searching and reading documents, I managed to find the files which define the JWM desktop. They are in /etc/xdg/jwm/.
One of the nuisances there was the 12-hour clock but changing the clock settings in system.jwmrc was enough to get it the way I wanted which is a 24h clock. Simply set Clock format %I:%M to %H:%M.
2a More tweaking: Partly succesful. Actually this is about another nuisance; the xterm does only work for user root and hence all applications which are started through a terminal window simply don't work for all other users. As far as I was able to investigate, it seems as if the values from the user's application.conf file are not propagated into JWM. Only the value for FILE_MANAGER seems to have an effect. When I changed this from the default (clex) to PathFinder, I was able to open a win3.11-explorer-like window from the System menu as non-root.
What I still haven't found is why the value for "TERMINAL" does not work in the same manner. Actually I'm still unsure about the whole setup. In applications.conf the variables are named FILE_MANAGER and TERMINAL. In /etc/xdg/jwm/menus.jwmrc I see lower-case parameters: file-manager and terminal. These can also be found via "which " so they could be binaries after all but by adjusting the value in the user's applications.conf I was able to influence the selection of the file explorer...?
I have said goodbye to slim altogether and so playing with a way to terminate Xorg because one cannot easily get back in there after switching back to the console screen. This is still work in progress.
/emgi