Just a note on 4k renders. I had crashing UE with 4k renders pretty regularly, because my comp was/is to weak… or rather, all the different sample settings, that worked fine for 1920x1080 resulted in to much payload for my comp at several 4k renders.
However, since 4.25 and Movie Render Queue, you can tackle this problem really well with the tiling function. So upgrading to 4.25 and switching from sequencer rendering to rendering with Movie Render Queue and it´s tiling might be something, you should consider for further projects 
Of course, this comes with it´s own set of problems, since not all effects work with tiling (like auto-exposure), but i am pretty sure, that most of them can be bypassed and compensated.
https://docs.unrealengine.com/en-US/…ort/index.html
Ok, you will still create all the sequences and cuts with sequencer and save them, just for the rendering you switch to that.
(i just don´t get, why they deactivate all those denoisers for tiling, i usually don´t touch them, but that prob needs more testing ^.^ )