The K-50 will give you good performances in low light and the DA18-55WR is a good start. It is regarded as one of the better kit lens across all brands.
I may suggest to start using the DA18-55mm. Then you can decide if you need a longer lens. You will have a number of options, incl. 2 lenses (eg 18-55mm and 55-300mm) or a single all-around lens. For travel, I would recommend strongly a single all-around lens, based upon my own experience.
If you are after a longer all-around lens, there are several options, including:
* DA18-135 mm WR - An excellent choice in my opinion; light, compact and WR (I value all these when I travel)
* DA18-270mm - A bit expensive and non WR
* Sigma 18-250mm - A bit heavy and non WR
* DA18-250mm - No longer manufactured, it can be found 2nd hand and it is still an excellent lens (a good all around lens well regarded across all brands)
Personally, I have both DA18-135mm and DA18-250mm. I find the Sigma 18-250mm too heavy for travelling, and the DA18-270mm too expensive.
To sum up, I suggest to use your DA18-55mm first. Once you are confident that you need a longer all-around lens, consider the above based upon your needs.
I hope that the comments may help.
Last edited by hcc; 01-30-2014 at 11:53 PM.