I did solve a part of my questions:
As reboot is available, to return to the LXPanel environment, only restart and in the Session manager Slim, hit F1 (eventually more time until the text "LXPanel" appears), enter into the system and you can choice a different Window manager according to your preference in the same way as you did choice the different one!
In JWM, to have quickly and easily a beautiful Applications manager, only install the package (and dependencies! sorry!) xfce4-appfinder ;-) ... you probably will not need more :-)) ! I did add a link to xfce4-appfinder with the shorter name "menu" ;-) !!!
But the question is not solve: where is the .jwmrc file to add the appfinder icon into the jwm tray (doing that, you can eventually make the tray auto-hidden ;-) in the tray definitions block ! or install 2 trays: one for the clock and the appfinder icon not hidden and one for the usual jobs automatic hidden (you can arrange your tray at the same side of the screen one left, one right, or an one of the other 3 sides of the screen! JWM is easily very flexibel. JWM is able to show a back ground picture without to need an other special application, eventually one picture per screen independantly from the other as 2 are set in that installation, and the .jwmrc can start applications, especially the setxkbmap so that you can forget the problem I did have with the keyboard setting! see pls at the bottom of that file!)! users working with xrandr to turn the screen 90 degre to make landscape print screens have to try the position of her jwm trays. test it before you decide and spend time into a complexe graphic arts presentation ;-) ...
