In reply to MalcyversustheMunros:
I back up my daily shots to a second card or USB stick using an OTG hub driven by an Android phone. Hubs only cost a few quid.
It was 2007 when I went to Mera Peak and there wasn't much charging available then, but I've had several Nepal trips since and each time more places have electricity. I'd be surprised if you can't rely on charging facilities as far as Phare at 5000m on your trek. Not at base camp or high camp though. Your trek organiser will know. Take half a dozen spare batteries for each device, and a charger that will charge several at a time. And a couple of powerbanks in reserve.
I have a 25W solar panel but TBH I haven't found it very useful. On a trek, you move on most days, with an early start, and by the time you get to the overnight camp the sun has lost its power and soon drops below the horizon (which being the Himalayas is a long way above you). It's less space, weight and faff to take extra batteries. If you were operating out of a basecamp which you would return to every night it would be different, of course.
I'm not familiar with your camera or Fuji lenses. I'd just say that weight and usability become more important the higher you go and the colder it gets. Something you can deploy quickly on the go will make it more likely you'll take a shot when you really don't feel like it. There's a lot to be said for carrying just a GoPro or similar (several people I know speak highly of the DJI Osmo Pocket) on summit day, mounted on a small gorilla pod, tied on and stored in a warm accessible pocket.
Compared with stills, even shooting dual RAW/jpg, video has at least an order of magnitude bigger storage and power requirements. I see from the spec of the spec of the X-T3 it can shoot video at 400Mbps. That's 3GB a minute! If you only intend to take a few clips of the view from the summit etc, it won't affect the advice people are giving on here. However, I am a filmmaker, and I have several terabytes of video clips of stuff it seemed a good idea to film at the time, without any clear idea of what I was actually going to do with it. And it's all too easy to hold on to shots for a minute instead of 10 seconds. When I've got home, there's never been enough to edit together a decent story. Nowadays I only shoot video when I have a proper plan for the film I want to make.
But if you do see a Yeti, or a snow leopard walks though the camp, film it, plan or not.