KDE provides a very large set of services. This makes it something of an elephant in the world of Linux desktop environments. Lighter DEs should fit in less than 1GB (that's anything other than KDE and Gnome). I think the last time I checked my system with just the DE up and nothing open, it was using on the order of 200-300MB. However, the lighter DEs will also do less by default.
It should be safe to kill baloo, but as others have already said, you will see some tradeoffs in how file searching works if you stick with KDE. If I'm not mistaken, it may restart periodically to index new files unless you go to some effort to exorcise it.