The last time I installed KDE and Gnome on the same OS (Opensuse 12.1), GDM and KDM started conflicting and they both stopped working properly and I was plagued with applications from both environments till the point the applications overview in gnome was flooded with useless KDE trash. Moreover, I still had parts of the KDE desktop appearing when I'm running Gnome (such as the password manager and kde fonts and some apps refused to give up the oxygen theme). If I install the plasma-desktop package on Ubuntu, am I at risk of having such issues? I just want KDE with the bare minimum number of applications; just the necessary ones to make things work. I'd rather not have dolphin installed either. Also, is it all right to install the kde-standard pack? Or should I just stick to the plasma-desktop pack?
I think it should work. You can try installing a package and if it doesn't work, you can remove the packages installed. Take a look at your APT log after you have installed it. All packages that were installed along with KDE will show up as one entry. To show it, just type this at the command line:
If your desktop is broken, press Ctrl+Alt+F1 to login. You can then remove the installed packages with:
sudo apt-get remove package1 package2 ...
Remember, even if your desktop is broken you can still fix it from the command line. The trick is knowing how to undo things.