I love Kdenlive, though it’s always worth keeping an eye on Openshot, Olive, Shotcut etc.
Is there any scope to allow the interoperability to work with multiple software on each end (i.e. Gimp or Krita with Kdenlive or Olive) - or does it complicate things too much?
For your first time, either is definitely good enough. They’re both pretty full featured, and they both follow “normal” editing conventions - so if you want/need to use a different program in future, you already know how to use 90% of it, you’re just looking for where the buttons are. It’s all very transferable learning.
As mentioned by another reply, there’s currently a lack of hardware acceleration for timeline playback in Kdenlive which means if you’re really stacking the effects up, you won’t be able to play back in the timeline at full frame rate until you pre-render. It won’t make any difference in simple edits.