I had a K-5 and now a K-1 with various lenses, all of which are Pentax. The lens I use most often is the least expensive of the new Zoom lenses, the
HD Pentax-D FA 28-105mm F3.5-5.6 ED DC WR Resolution on this lens is as good as the more expensive f2.8 24-70. The trade of is that it is a slower lens, so not so good for portrait etc when bokeh is a consideration. It's not as wide, but does have longer reach. Importantly it is far more portable, and perhaps that is why I use it so much. I also hear that Pentax are going to release a 70-200/4.0 which should be complimentary to the 28-105
My first new primes were the two you refer to, 35/2.4 and 50/1.8 - they are excellent value for money and quite pocketable.
If you're on a budget, there are so many legacy primes that you could snap up. The manual focus A series and autofocus FA series are my favourites, the former being quite affordable. I particularly like the A 20mm and A 28mm.
Importantly you can use all your DA lenses on the K-1 with crop mode. A few, like the DA 40 and DA70 more or less give full frame coverage.
If you want a really sharp standard lens, the D FA 50mm f2.8 macro is worth a look at. If you want a good portrait lens, the DA* 55mm f1.4 SDM is a really good with only minimal vignetting when wide open which can easily be corrected in post processing. You can see sample photos of these and most other new and legacy lenses on the Pentax K-1Laboratory. Here's a good example of
what the DA* 55/1.4 is capable of It's an expensive lens new, but used they are good value for money. It's nicer to use than the FA 50/1.4 and is WR if that's important to you.
My advice in a nutshell is that you pair the K-1 (which is far less expensive than the K-1ii) with a HD Pentax-D FA 28-105mm F3.5-5.6 ED DC WR and work with the lenses you have first. Then if you want more or better primes, consider used lenses as a way to buy better for less $$$. Good luck.