Is there any way to keep the settings of XTerm that I've applied so that it opens with these settings when I reopen it (e.g. text size, set by Ctrl+RightClick)?
You can either launch xterm with the relevant option (see man xterm) or create an ~/.Xresource file with the setting there. Try running this command:
echo "xterm*font: *-fixed-*-*-*-12-*" >> ~/.Xresources
That will append xterm*font: *-fixed-*-*-*-12-* to your ~/.Xresources file (creating it if it doesn't exist), which is read by xterm when it starts. If you now log out and log in again, (or just run xrdb -merge .Xresources) your xterm will have its font size set to 12. For the various other options you might want to set, see man xterm and add them to the ~/.Xresources file.
NOTE: This works as expected on my Debian and I used this approach for many years and on many distributions to set the various settings for xterm (and aterm which you might want to check out by the way). For some reason, I can't get it to work on my Ubuntu virtual machine but I am hoping that this is specific to my setup. I'd be very surprised if it doesn't work on Ubuntu.
