Thanks guys (and
@twist). Using AF onto an object some distance into the scene is only going to work sometimes (ie if there's a suitable object!), though it's nice to know there is a DoF indicator so at least you'd have a clue of the near and far limits.
I get the impression that using MF with these lenses is pretty tortuous (very low focus gearing?), unless you use the "AF then fine tune MF" approach (can't remember which back button does this in MF mode). But again, the latter's only going to work with a suitable object.
So: both distance and DoF markings? If so, the 14 would seem like a good choice to learn hyperfocal distance focusing on!
Using a legacy manual lens would obviously be a good move. Unfortunately the 1.5 crop factor turns my not-very-wide 28mm into an almost-normal 42mm, and I haven't read paeans of praise for Pentax-X adapters either. And <20mm Pentax lenses seem humungously expensive!