First off get the K1 before worrying about extra lenses. Your current kit, apart from a wide angle is fine. So having first got your K1 a wide angle option would be a priority. Maybe a 24-70mm or 28-105mm. However, the K1 is a fantastic piece of it to use with vintage K mount glass which mostly can be picked up at a reasonable price. I would consider the K 24mm f3.5, K28mm f3.5 and K 35mm f3.5. A more modern option would be an (HD) FA 35mm f2. This is a very useful lens which doubles up as a standard on your K3 iii.
For longer reach on a budget consider the F 70-210mm f4-5.6 or A 70-210mm f4.
As standard lenses the K 50mm f1.4 and F 50mm f2.8 Macro perform very well on my K1.
---------- Post added 05-11-23 at 03:46 PM ----------
Originally posted by Sjak This was also more or less my reaction to the opening post.
I don't really see a motivation for buying a K-1, except 2-3 lenses that also work on FF (meaning the other lenses don't)
The 16-50 was mentioned as walkaround lens for APSC, but I didn't see any reason why this lens does not satisfy for this particular user case.
Of course, if there is a strong desire to purchase and develop a second system, that's cool, camera&lens-collecting is fun, although it's something mostly unrelated to photography. To be clear: I own maybe over 100 lenses so I don't have a negative intent with this comment; it's simply good to be honest about the purchase motivation: A new lens or new camera won't make us better photographers, but the chase can be lots of fun.
It took me years of prevarication before buying my K1 in Oct 2021 for the same reasons you state here. When the K3 iii was released I was very enthusiastic over the thought of getting one, but did not want to lose either my K3 or KP to help finance the purchase for a camera which for my needs at least the K3 iii's capabilities were overkill. I luckily had the opportunity to try out both a K3 iii and K1 ii side by side and it was abundantly clear to me that for slow considered photography the K1 is a much better tool and would add to my enjoyment of taking landscapes and still life. So the K1 ii was acquired. Luckily being a fan of vintage K mount glass I already had a good range of lenses to use on the new camera. I soon discovered that using them on the K1 is much more satisfying than using them on an APSC camera. So whilst I broadly agree with your point, I do think that there are circumstance that a new system (which the Pentax K1 is not really) or piece of kit can add to one's enjoyment and lead to images you would not of otherwise taken.