ruud, welcome to the forum.
Firstly, I can suggest that you utilise the forum's
Pentax Reviews - Pentax Lens Reviews & Pentax Lens Database section for general advice on the lenses of your choices. There are also
Pentax Lens Reviews | Pentax in-depth reviews | PentaxForums.com for further knowledge of Pentax lenses.
Secondly, the lenses you listed above are good for some portraiture, but not very much in the way of landscape photography. They're not wide enough. If you do not already have the 18-55 kit lens, you could consider that one for starters as it is very cheap (but not bad in terms of quality). However, a step up from that lens for landscapes is the DA 16-45, which is also not very expensive, but a substantial increase in image quality. If you are more interested in prime lenses, then you will need to invest more into a wide landscape lens such as the DA 15 or DA 21.
Portraiture is another story. The FA 50 may do you well overall, but the DA 35/2.4 is a cheaper alternative and I think at least as impressive as the FA 50 at all apertures. It's a matter of knowing what your preference is in focal length. Tighter crops of head and shoulders means an FA 50 would be better suited to you than the DA 35, but full body portraiture will be easier with the DA 35. If you would also consider manual focus lenses, then there are a number of cheaper possibilities in the 50mm range of M or A lenses - it's just a matter of finding one. The forum's marketplace can be a good place to look for one of these.
All the best in that.