Newcomer SW advice
As an Aperture and PSE user (as well as K-5) I can add that while you definitely can just use PSE to get RAW files into shape and export as whatever you like, it really isn't a great environment for doing a lot of work in. For occasional use it's fine. My daughter uses it for her stuff, also Pentax and RAW, but she only does a few images out of her whole shoot and uses global, broad strokes only. Every once in a while I do a few there also, just for the heck of it. But that's about all I care to do. If you have a few hundred images every few days I would say you should get a program that's built for it. Aperture is a hugely better workflow once you go past the few shots every week. All the caveats apply (When will it be updated? What is its future?), but it's the best way to spend $80 and have a good RAW working environment.
Wait until after the 11th, when the WWDC conference starts, when Apple's expected to make many announcements, hopefully including some Aperture news.