We have hedgehogs wandering my neighborhood at night.
The younger ones are pretty friendly and rather cute.

I use the 8-15mm f3.5-4.5 on my D500 and it works great.
Only limitation is that you can't zoom out past about 10mm (the point at which it becomes a circular image on your D850).

I find that when shooting with my 58mm f/1.4,
if I want to shoot wide open at ISO 100 and 8000 shutter (max on my D500) in full daylight, I am still sometimes over exposed.
I could close down the aperture, but that would affect depth of field.
So instead I reduce the exposure compensation as necessary.

Since all three of the settings in the "exposure triangle" will affect visual elements of the image;
higher ISO introduces grain, shutter speed affects any movement in the subject, and aperture affects depth of field (and depending on your lens, also effects vignetting, chromatic aberration, etc.),
exposure compensation allows you to adjust brightness/darkness without affecting these settings.

At least that's my understanding of how it works.

Would it be 'drip your drops' ?

D500 doesn't handle high ISO?
I've only heard and experienced the opposite.

Reminds me of my friend's wedding: hilltop wedding in Marin County... rained and super-windy: would have been nearly impossible to photograph without subjecting your gear to some pretty harsh conditions.

Just a reminder to prepare for inclement weather (Norcal summer is no guarantee of sunny skies).

Perhaps take portraits with and of my closest family and freinds.
It would give them something by which to remember me.

The Nikkor 60mm AF-S Micro is a highly recommended macro lens for Nikon, and also useful for digitizing slides.

I have the Nikkor AF-S DX Micro 40mm f/2.8G - which is about half the cost. With an extension tube, I pretty much have to manually focus or it just hunts forever. I do like that it's very small/light, and when combined with extension tubes, I can get with an inch of my subject. I think it would be pretty difficult to work with a large/heavy lens when shooting macro, even with a tripod.

The more expensive Nikkor Micros (105mm and 200mm) are bigger and heavier, and have a pretty limited field of view (and are more expensive): so if you just want to take pictures of an insect's head, those might be cool, but for the full insect, 40mm or 60mm might serve you better. Sort of depends on your subject matter.

I assume the OP is referring to Extension Tubes, rather than a teleconverter.
Since these don't have any glass in them, you really just want something that has the electronic connection pins so the AF in your lens works.
I bought these off Amazon and they work great:

https://www.amazon.com/Mcoplus-Extnp-Focus-Extension-Cameras/dp/B00ORLQJR6/ref=sr_1_1_sspa?crid=2UG39M1BNMD0Y&keywords=extension+tubes+for+nikon&qid=1583413757&sprefix=extension+tub%2Caps%2C235&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzSTdQVFBRTExQWjM4JmVuY3J5cHRlZElkPUEwMTE4NjczMjRZSjU1S1JZNTdORCZlbmNyeXB0ZWRBZElkPUEwMjgwODM5TTE5OEhLQVE4SU9BJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

I'd get the D500 since you already have a D810.

I see my gear kit as a toolkit: with different tools allowing me to craft different images.
Unless you're a pro who relies on having a backup with identical specs, why not get a tool that allows you to specifically create different images than your current kit already allows?

Then you can use the D810 for landscapes and stills, and the D500 for birds and sports.

... looks like the D500 is also a bit cheaper.

I was a bit underwhelmed by the specs when they were announced...

With the D6, you're paying for a lot of features related to professional workflow: specifically developed for photographers at events to get their best images published as quickly as possible.

From Nikon's D6 overview:
https://www.nikon.com/news/2020/0212_dslr_01.htm

"The D6 also contributes to a faster on-site post-shooting workflow that is so vital to professional users. It does so with new functions that enable faster transmission of decisive photos, including one that allows photographers to transmit their winning images first with a flick operation using the camera monitor that moves the current image to the top of the waiting list*2, and another that enables simultaneous recording of two JPEG images with different size and quality settings — a smaller one suited to transmission and a larger one for editing, for example. What's more, the D6 supports the same 1000BASE-T Ethernet standard as the D5, with an approximate 15% increase in its transmission speed. Together with the built-in Wi-Fi® capability, it makes for a complete response to the wired and wireless networking needs of professional photographers. Further, equipping the camera with a GPS function*3 enables acquisition of accurate date, time, and location information."

I also have the Sigma 150-600mm and find it to be softer than I'd hoped for, especially when fully extended to 600mm. Still, I've taken many sharp images with this lens, and find that avoiding the extreme focal length helps a lot.
I'd like to sell it and get the Nikon 200-500, but that will likely have to wait until I'm back in the States and have extra funds to spend on the upgrade.

Unboxing videos are popular for a number of reasons beyond self-absorption.
Among other reasons, people want to verify a company's product and quality, as well as confirm the accessories that are included.

Unboxing videos might make less sense for established companies like Nikon, Sony, and Canon: where the brands' reputations are well established, but for many products that are pitched and purchased online, many people are rightfully skeptical.

There are certainly psychological effects as well: for me personally, when I'm assessing a new lens purchase, I want to know as much as I can about the prospective lenses I'm considering buying. For me, these are fairly significant purchases, and unboxing videos performed by experienced photographers who review the lens in the video help be understand build quality, weight, size, etc. Since I don't live in an area where there are camera shops where I have access to seeing lenses in person, these videos give me a better sense of the lens.

For some, it also provides the virtual experience of buying a product that they wish they could afford, or anticipate buying in the future: a sort of fantasy, or even as a temporary remedy for a severe GAS attack.

I agree that many of these unboxing videos are pretty useless: videos without any commentary or review of the lens were likely made just to rack up YouTube views and earn money off the ads. But their popularity demonstrates that they are far more than self indulgence on behalf of the video's creator.

"Zoom with your feet", they say.
But you're right, it's a different picture - as you move away from an object, more of the background comes into view (and vice versa).

Bugs me everytime I hear it.

Hmm... if you're saying that anything shorter than 15mm is the same in a fisheye as to a standard wide angle, I feel this is quite inaccurate.

There's a big difference between how my 10-20mm wide angle renders images at 10mm than how my 8-15mm fisheye does at the same focal length:
specifically, the fisheye bends lines while the wide angle is 'rectilinear' (keeps the lines straight).

See these two examples taken at the Taj Mahal from nearly the same spot at about 10mm each.
Pretty noticeable difference.

As a lacrosse player, the best shots taken of me were from the end-line by a photographer standing behind the goals, though I'm not sure they'll let you stand there for safety reasons. If they do, you might even consider wearing a helmet (not joking).

Otherwise you're shooting from the sideline, which is going to be tricky, since offensive players nearest to you will be mostly facing away from you, and those facing you will be on the opposite side of the field with defenders in their way.

200mm is pretty good reach, and 2.8 is wide enough to get good light.
Seems Jaackil has some very good points about preparing for your task.

Good luck!