What should I upgrade to from a Nikon D7200?

I have a Nikon D7200, a 50mm f/1.8G, a 18-140mm f/3.5-5.6 and a sigma 18-35mm f/1.8. I'm planning to get a new camera(and maybe a lens or two if needed) as an upgrade to this one but I'm confused to which I should get. I really like the new mirrorless cameras coming out like the Sony a7III, Nikon Z6 and the Fujifilm XT-3(or if any other choice is better). I need a recommendation on what to get with a budget of $3500. I also don't want to sell off my D7200( though if it is more beneficial you can say so(I'm currently living in the Netherlands, so keep that market in mind if that is the case))
Things I want are:
1. AF better or on par with my D7200(better especially in video)
2. Good lens support
3. Good 4k video
4. Less weight than before( so that I can take it on a vacation or something)
5. Good EVF (I've never used one though)
6. Good battery life or batteries being cheap
7. Sensor stabilization(I don't have anything other than a tripod)
8. I might do some vlogging
9. I'm a casual photographer doing jobs on the side(though that s rare). Mostly for myself and friends and family.
10. I'm not sure about eye-AF though I did hear it's great.
11. I'm very nit picky though on pictures and video though
12. Maybe some accessories
13. I could do some astrophotography and time-lapses
14. I could jump into professional work but am not sure at the time
Anyways, thanks for reading through all that

Upgrades are nice but remember - no matter the camera - still or video - the final results are really controlled by the users skill with lighting and composition - not the camera choice.

A full frame DSLR from Nikon or Canon should serve you well.

Besides 4k video, there's not much to choose from as far as an upgrade. Your camera is pretty darn good. Perhaps a D500 or full frame.

If you want mirrorless, probably can't go wrong with the Sony a7 series or a6500. You'll need to get new lenses as your Nikor lenses won't work with a Sony mount. Compared to a DSLR, battery life isn't as good on a mirrorless. A DSLR will get over 1000 shots per charge.

If you say you're picky about video, then forget the above toys which will only do 30fps 4k video. Get something like a Sony Z280 with 3 sensors. That will shoot 60fps 4k video. Of course, there are other 4k 60fps camcorders in the $3000 range.

Besides having a new toy to play with, as Bernd says, your skills are the limiting factor in your image.

Whatever you plan to do, stick with one camera system, and, if you have already embarked on Nikon DSLR, stick with that. We have no idea what you find exciting, but I note that you don't mention accessory equipment. The first item to consider seriously is a good tripod (portraits and astrophotography) plus multiple remotely fired flashguns (portraits).

If you consider extra lenses for fun then the quickest way to fun is the fisheye lens for spectacular wide-angle distortion pictures, or a dedicated prime macro lens for real close-ups

Nikon lags in video work, although if you learn the limitations of whichever body you use, it isn't unusable. Good video work does not rely on autofocus at all.

For you, a D500 and a 70-200 f/2.8 would both add to your kit and possibly bring more "fun" to it as well. Nikon has full frame models, and unlike some other makers their DX (crop frame) lenses work just as well on full frame bodies. So a D750 or D800 would also be something new and different.

If the D7200 is too heavy to take on vacation (really?) then nothing from Nikon is going to replace it. The Sony A7-A9 bodies are smaller and lighter, but their (good) lenses are still as large and bulky and heavy as what you are using now. They are much better at video than anything from Nikon, but you still want to avoid autofocus!

Eye-start focus is one of those things that you either really like, or really don't like. My Sony body has eye-start focus, and I keep it turned off most of the time. The issue for me is the camera starts to focus before I have what I want to shoot in the frame, and if it picks something close when what I want is further away it then becomes an issue trying to find my intended subject.

It's really a toss-up. If you switch makers, you have to start all over with lenses and accessories other than tripods and the like that are maker independent. That can require more than your budget allows to regain what you have now.

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