Full KDE metapackage (that fast and easy way) will install a whole lot of stuff you probably don't want. Removing the unwanted stuff is a hard, complex, time consuming and annoying task. apt-get purge for the individual packages won't do a very good job. Many files will be left behind in the HD. Better install selected packages in advance. The ones you actually want to have. Installing Kubuntu desktop is possible and will be a decent smaller package than full, but it's "plain KDE", not the tweaked Linux Mint KDE version... which is superior, IMO.
After doing it a lot of times. I don't like installing and mixing DEs in a single OS. Unless you are very limited of disk space I much prefer adding another relatively small partition and building a dual boot system with the two flavors fully independent. They will work as they should without compromises and mixed things. Login out and in for a different DE session won't take much longer than rebooting into a separate OS. What I do to keep a "single home folder" is using the very same user names and IDs. I leave the Desktop and hidden files alone for both OSs. Then for one of them I make links for all those other folders; Pictures, Videos, Music, etc... so I only kinda use one home folder for both systems. But both have their own configuration files. Oh and I sync the .mozilla and .thunderbird folders too.
I don't have such a system right now. Just KDE. But it worked fine for me for some time when testing what distro and DE to choose. Finally settled in LM 15 KDE.
my 2 cents.