Well, I have quite an assortment, now. That wasn't intended, as the K1 (now upgraded) was purchased as a backup camera for my Z, and for UWA situations. But I have grown my system to be fully independent, although I use the cameras in tandem now for professional work. For my personal artwork I have only been using the Z, and for family I have only been using the K1U2 (what I call it now). So here's my rundown:
Irix Blackstone 15, purchased for the UWA work for interiors. Low distortion, excellent lens. Purchased new.
Pentax 15-30, purchased because it was on sale at the lowest price ever, new. Same reason as above, with a bit more flexibility. Haven't needed to use it much yet.
Pentax FA 20, purchased for reasons as above, and because sometimes really 20 is as wide as you want to go in a museum---even if the Irix doesn't distort much barrel wise, there's still that s-t-r-e-t-c-h at the edges---very bad for art objects. Also, for a lens this wide it is very petite! Very nice lens, underrated IMO.
Pentax 24-70, same reasons for purchase as the 15-30, also new, and a "one lens" solution if that is necessary. Useful for the odd event I have to shoot. Very good lens.
Pentax 28-105 WR. Light, small, useful, fantastic walk around lens, and weather resistant. Tremendous value. Much better than it has any right to be for the price. Some reports of shutter shake/shock exacerbated in this lens, I haven't seen it myself.
Several Pentax 28's----got 2 of them for my previous A7R, an M and a K, the K is better but larger. Might sell them though, now that I have the other options. Have always liked the 28 focal length, personally. Also have the 28 shift. Keeping that one.
Pentax 31 limited. Just got a great deal on a used one, so I snapped it up. Wasn't going to buy one due to their high cost, even used. Quite interesting focal length.
Pentax FA 35 f2. Had this before the 31. Excellent value lens.
Pentax A 50 f1.4. Have this for bokeh, infrequently used because what I do mostly requires deep dof. But these are very nice lenses and available cheap. And when you need bokeh....
Pentax FA 50 macro...for macro when it is required for work. Excellent lens, excellent value.
Pentax 77 limited. Another great deal I got used, and one of the very best lenses in the Pentax line. For portraits, bokeh, and isolation needs at work.
Pentax 100 macro WR. Again, for macro when required, and short tele or long portrait, isolation. And it is excellent, so small, fast-ish, and weather resistant. Another excellent lens, and excellent value.
From the list above you can see what my shooting involves. I rarely if ever do tele. For that I have several of the 645 lenses, including the A* 300, which I can use with an adapter on my K1U2. I also have the tele converters for the 645 lenses, which then also work with the adapter.
This is a very great thing about the Pentax system, and it gets short shrift or is forgotten entirely, even by Pentaxians!----the ability to go vertically from 6x7, through 645, to FF and then APSC with downwardly and a few upwardly compatible lenses, and it's all backwardly compatible as well, plus the flashes work across all formats, along with several other accessories. Canon and Nikon brag (somewhat rightly) about their systems, but no one else in the industry can do Pentax's trick. And for overall value, no one beats Pentax (although in medium format Fuji is definitely in the race, now, although there is no back catalogue of used lenses, and won't be for years).
IMO, Pentax has the best total system any manufacturer has ever assembled.
