You could of course just add -vala to make.conf or something such, but I like to keep my settings sorted according to what requires them like I did above.
Now for installing the desktop environment:
(chroot) # ##i##echo "media-video/ffmpeg -chromaprint -frei0r" > /etc/portage/package.use/ffmpeg
(chroot) # ##i##emerge --ask kde-plasma/plasma-meta
Now you are done. Enjoy your laptop with Funtoo.
In case of some interested party, I am continuing with some tips that may prove useful to setup a light system with dropbox. I put very little effort into making it look pretty, so you may want to press EDIT in the wiki to get source of the page for a more readable version.