Having jumped in boots and all into KDE on mainpc (having had to reinstall Debian and choosing KDE instead of XFCE) there are a few things to be aware of. At least we do get 5.8 version of KDE Plasma on Stretch, I would have half expected it to be 4.x because of Debian’s reppo for older versions of stuff but having a 5.x release is good, of course I would want 5.13 but maybe Buster will have something like it when it comes out next year.
The standard KDE install task from Debian is only a minimal desktop that lacks some useful stuff and it also defaults to an ugly looking logon screen with Debian wallpapers. On my test config I installed extra packages for the breeze login theme. I had to install synaptic package manager to find them as the KDE software centre could not list them.
To make life easy you can install kde-full package which just puts all the KDE stuff in because Debian doesn’t do this at install time. This will overcome numerous frustrations and trying to figure out why something doesn’t work like it should (like the printer not being detected when you plug it in). Probably this situation is no different from other desktops like XFCE not being completely installed, the difference is there is so much more in KDE that you are going to be missing out on a lot probably, there something like 500 packages left out. OK you may not need them all but if you have a powerful system and are not too worried about bloat then it is probably easier just to install the whole lot at once.
After getting these extra packages installed the printer was straightforward to get going and print from. I have spent much of the evening tweaking various KDE things and really getting up to speed on it which has been slow but tomorrow I will get some real work done as I have really lost a day but unfortunately it has been that kind of week of getting very little done overall.