If you have to ask us if you really need this lens, do you think you need it? I don't think so.

Low light, high ISO is one of the reasons to move to Full frame camera. You said it is your primary concern, I don't understand why you are even considering crop sensor camera. With FF you will get at least 1 stop of light more than with Crop sensor.

Hmm..., I've been using this flash for 2-3 years with my Nikons and it works in Auto and Manual modes without any problem. Don't know what to tell you. I would try to do reset on your D7200, hopefully it helps.

What do you mean set camera for snapshots? Do you mean Program mode?

Here is another one: Nikon AF-S 12-24mm F/4 G ED.

It’s DX lens, it’s been in production since 2003 and you can still buy it new, but they are very expensive-over $1000. There are many available used for around $300. I bought used for my DX body a month ago and like it a lot. Very well built, internal focusing, while zooming the length of the lens does not change. My favorite part is - it works quite well on FX body from 18 through 24mm range.

https://www.opticallimits.com/nikon--nikkor-aps-c-lens-tests/757-afs12244dx

My prints from Nikon D70 (6mp) still look very good.

I have this lens and use it all the time on D5500. I love, it works great, VR really works. Tell your friend he will not be disappointed with 18-140.

Dual card slots?

I use Photos sometimes when I shoot Raw. It's okay program, the Noise Reduction and Sharpening are pretty weak, everything else seems to be okay.
I can recommend PhotoScape X. It's free program, VERY easy to use and way more powerful than Photos. Another free option is Raw Therapy, but PhotoScape X much easier to use.

This is an interesting video. Landscape photographer who mostly shoots RAW had a challenge to shoot JPG with no edits allowed. He created in the picture style menu a profile that suits the scene.
I think he did very well with the challenge, especially I liked his second image.

https://www.youtube.com/watch?v=AA3_Su-HTrQ&t=8s

I think this advice is good. In mid May it's hard to plan, it could be nice or could be rainy and cold. Once you come to Seattle and know the forecast you will know what to do.
I suspect that it will be mostly street photography. Check the East side: places like Bellevue, Kirkland. There are lots of nice places around Lake Washington. In Seattle there is nice area by the Lake Union. They have SeaPlane flight for 20-30 minutes if I remember correctly.
Boeing offers public tours, I think one of the locations is in Mukilteo, about 25 miles north from Seattle. In Redmond (East side) you can visit Microsoft Visitor Center (if you are interested). You can easily get more information on that on line. Welcome to WA.

The only Fuji lenses I have - 18-55 and 55-200.

I am shooting with X-E2s. Recently I wanted to treat myself for my birthday with XT2, very popular, great camera. I took several shots with both cameras using the same lens trying to keep the same settings. After comparing the shots I decided to keep my X-E2s. Yes, it is not the right camera for tracking moving subjects but the IQ that comes from it is just excellent. And yes, 16mx is more than enough for most of us.

If you are using Apple computer you can do it in iMovie, its quick and easy.

I was there long time ago, during film days. I think it's good to have all purpose zoom, like 18-200 for DX or 24-120 for FX camera. Also take one fast prime, 35mm f/1.8 for low light. I remember in the rain forest could be quite dark even during the day.