You need at least one fast lens like that. So if you're not planning on picking up something like a DA*55, FA77, or FA31 (which are all excellent) anytime soon, you should keep it.
Rather than selling the DA50/1.8, I'd add a DA35/2.4 and practice using it wide open. Then start saving up for a used DA*50-135 or a FA77 (assuming you don't have the budget right now).
The K-3's a very good camera. Within a reasonable amount of time you'll be building a lens kit that costs 2x or more the price of the body, I trust. In the mean time, find an A100/2.8, K50/1.2, A24/2.8, K200/2.5, or something like that. I doubt you'll be wanting to change systems.
If you have any hesitation in spending more right now, the Sigma 17-50, DA50/1.8, DA35/2.4, and F70-210/4-5.6 (used - either Pentax or Takumar version) are quality lenses that are a great way to get familiar with the system.
Last edited by DSims; 04-16-2014 at 12:00 AM.