Looks pretty solid! I’m a fan of the air cooler, I’ve built with both and after having the pump fail suddenly on my AIO I won’t use anything other than air.
One thing to double check would be RAM clearance for your CPU cooler vs the height of your RAM. Idk if pcpartpicker checks that and it would suck to get into your build and have it not fit correctly.
Shotcut is a great easy to learn video editor I have used a lot.
Yeah mobi support got removed earlier this year. Epubs work fine for me though once use calibre to remove the DRM.