I am surprised that you have CA issues with your 31ltd even with f8 and higher.
I tend not to get issues from f2.8.
The thing about the FA31 and 77ltds are that they do tend to have much more CA if slightly OOF (or that the DOF is not enough to draw over the subject properly), so focus can be an issue here too.
I did not really like the 31ltd that much on APSC.
Too tight a look for the money and the uniqueness of the lens does not shine thru imho.
On FF, the central sharpness between f1.8 to f4, the wide FOV and engagement distance, the falloff from the center, all contributes to that "pop" in the images (much more than apsc).
BTW, I think your 31ltd most likely has issues and you should return it.
There are pros and cons to the K1 vs K3 and even more so the KP imo.
The K1 is certainly bigger and heavier, so if you are looking for smaller/lighter gear, it may be a factor.
The K1 does make shallow DOF for isolation type shots easier.
Landscape wise, nowadays, I am tending towards the thinking that if you can live with "enough for most needs", apsc isn't bad at all.
A Sigma 8-16/10-20; covers it usually. (more limited in the 14-15mm equivalent range than FF though)
Ironically, I do think FF has more UWA choices (esp primes) in the DFA15-30; Irix 11mm, Laowa 12mm, Samyang 14mm, Irix 15mm.
But we really don't need that many lenses in practice...
If going for the K1, for your needs.
Samyang 14, Samyang 24, FA50/1.4; DFA55-300 (in crop mode) should suffice for now.