I would definitely stick with the camera body you have for now, while you see how the hobby evolves. Although an older camera, it's still capable of taking great photos - and there's really no need to trade up until you find yourself pushing the limits of what it can do. There are folks on these forums using Pentax DSLRs older than your K-x that produce fantastic photography with them.
The two manual focus lenses you have are an excellent set covering many use cases, but as you've found out, manual focusing on DSLRs can be challenging. If you're in a position to spend a little money, I think you'd do well to consider buying one or two auto-focusing lenses - inexpensive enough that you're not committing too much at this stage, but with good enough optical performance that you'd still use them if you should subsequently buy a newer camera. The DA21 is, indeed, a very fine lens, and an excellent all-rounder for landscape, architecture, street and general photography. I haven't used the DA*55/1.4, but I love what I see. The field of view makes it a perfect choice for portraiture and situations where you want a little more reach.
For general use, you might also consider a 35mm lens such as the inexpensive DA35/2.4, or the more expensive DA 35/2.8 Macro Limited. Both would be extremely versatile on your APS-C K-x.
Alternatively, you could choose one good zoom lens - something like the DA18-135 - so that you have the opportunity to try out a wide range of focal lengths. In time, you'll find where you tend to shoot most - then you can look at picking up a prime or two