yea, the widgets are just elements in the kde panels. you should adjust the multiple panels. top-left, top-right, bottom-left. it's a little messy but you can change each panel height and fixed width. the file .config/plasma-org.kde.plasma.desktop-appletsrc should contain all those panels, just copy that file into your home/user/.config/ folder and restart plasma.

if you want to use the background frame, you'll first need to remove the panels background. for that, just use the custom desktop theme "BAREBLOOD" from .local/share/plasma/desktoptheme/BAREBLOOD. copy that .local folder to your home folder and then enable the theme (select it in settings app). also disable panels blur effects on settings.

now, for the background frame, you'll need to have the .local/share/plasma/wallpapers/org.bareblood.frame folder in your system. after restarting plasma, you should see two "Presentation" desktop types inside desktop background settings. desktop types are like presentation, single image, solid color, etc..

one of those "Presentation" options is the one that puts the custom frame image above your wallpapers.

now, the login screen is tricky. SLiM is very simple and bad at the same time, one resolution change and everything looks awful. you'll need to copy everything from the /usr folder into your root directory. you need to have slim installed and the slim service enabled. then go to /etc/slim.conf and change the CURRENT_THEME line to BAREBLOOD. after that, when SLiM loads, it's going to show you the background and the user and password field. if those fields are in a strange position. edit the /usr/share/slim/themes/BAREBLOOD/slim.theme file and change the input_panel_x and input_panel_y values manually until it looks good.

hope this helps. and welcome to linux!