i think it has been said, but: what focal length to use for what purpose is mostly bs. who said you can't shoot landscapes with a short tele? or a long tele. you can do whatever you want, experiment, and don't worry about rules so much. (i'm sorry, i no longer have pictures online to show examples)
wide angle: 18mm on apsc is not at the limit, it's "right in the middle", it's a respectable wide angle (like 28mm on 35mm film). a 24mm would be a "mild wide" on aps-c. a 16mm would be in the realm of ultra-wide already. Beware of wide angle lenses, you need to learn how to use them effectively, otherwise the pictures will not be making any sense. i suggest to start with this idea: a wide angle requires a foreground, subject, and background. the foreground is almost always not optional
for instance, two rather boring pictures, taken in the same area (grossglockner hochalpenstrasse -- hey, don't tell me, tell the austrians):
http://www.alpy.net/grossglockner/obr/glo_206.jpg https://www.pentaxforums.com/gallery/images/3491/1_K20A9851-watermark.jpg
they both seem to be shot with a wide angle (i guarantee for the second, as i shot it), but in the first you can't quite tell if it's a wide or not, and it has that "meh" look about it. Now mine is not something to make you sit up either, but you can see the foreground gives it some "depth", this is one of the "magic" things about wideangles. Until i figured this out, i hated wideangles with a passion.
the pentax kit lenses are generally very decent, so you will find it hard to compare the iq to old primes, but it is, almost always, better for the primes. add to that the elegance, size and "pleasure to use" of the primes, and you'll see why many people are addicted. however, this does not mean they are for you, you might be fine with the zooms and take great pictures with them.
landscape/dynamic range: i happen to hate the hdr look, what i do (used to*) is to use a little piece of software called "enfuse", it is part of hugin, and it is great (it manages to do exposure blending in a "reasonable" manner, to my eye, without the tone-mapping insanity). hugin is worth having a look at in any case (probably the best software for panorama around these days, and open source)
* used to because, since i switched from k20d to k-5, i ended up taking "one shot" instead, the dynamic range improvement was so dramatic for my needs that i found myself leaving the tripod at home at times, and trying higher iso handheld (yeah, i know, blasphemy, i was having fun though); having said that, in extreme situations, using something like enfuse to bring the dynamic range of the raw into a jpeg might still be worth it.
bmx bike: interesting, i must consider a trip to new york one of these days. everywhere else in the world we call that a wheelbarrow :P