I bought a refurbished Nikon D850 from nikonusa.com at the end of 2018, and it arrived with a shutter count of 30 right out of the box. Never had any problems with any of the refurbished Nikon cameras I've purchased directly from Nikon.

I suggest you consider contacting The Camera Doctor in New York City. He's helped repair two vintage Nikkor lenses for me, but I am sure he can help with your camera: https://www.cameradoctornyc.com/

I always carry a Playtex Living Glove in my camera bag to help un-screw stuck filters... It's always worked for me.

I you wish to remain within the Nikon system, I suggest you seriously investigate the "legendary" Nikon D500, which excels at fast auto-focusing and shooting, and can be used with both FX and DX Nikkor lenses. Check the reviews and videos online!

Sounds "classier" and more "artistic" or "elegant" than photo, picture, pic or shot... They're all interchangeable at the user's discretion.

Here's a useful Back Button AutoFocus guide created by Steve Perry which I've used to set up both my Nikon Df and D850 for BBAF... Now I prefer back button focusing versus using the shutter button.

Attached file:
(Download)

Like other responders, I too would advise a longer lens for your macro photography, which will allow you not to get too close to the object you're shooting... especially bugs which will tend to walk or fly away if you get too close with a short lens. I recommend either the AF-S VR Micro-Nikkor 105mm f/2.8G IF-ED. If you want to save a little $$$, the 100mm Tokina Macro AT-X Pro D is also a fine lens which many photographers prefer to the Nikkor model. Either way, you can't go wrong.

I have two Df's and for basic fill-in flash I use a Nikon SB-400 Speedlight or a Nikon SB-700 for heavier-duty needs. The SB-400 is a nice little compact and lightweight unit with a "low profile" that looks great on the Df. And although it's now discontinued by Nikon, you can find used ones on eBay, generally for less than $125. There are currently quite a few listed on eBay.

Nikon SB-400 Speedlight

The second one...

Sounds like a good excuse for a road trip!

Congratulations on the killer price you paid for your purchases. This is the reason I've created a list of all my new and used photographic gear purchases (including dates of purchases, prices paid, condition at time of purchase, retailer, serial numbers and photos) currently valued at over $25,000 -- so my wife will have this information when I die and has to liquidate all this stuff and hopefully not get too ripped-off.

Was Pelosi eating ice cream when she said that?

I bought a new D810 at the end of 2017 when it was being sold with a free battery grip and used it for about a year. I was never that happy with the photos it shot versus the Nikon Df camera I also have. I was annoyed that the D810 didn't auto-focus as quickly or accurately as the Df. So when the D850 was introduced in 2017, I waited for Nikon USA to sell a refurbished one on their web site, and I bought one in late 2018. I've been using it for over a year and I love it. I encourage you to re-think the D810 and find a nice pre-owned or refurbished D850. The D850 is considerably better overall -- and as a "legendary Nikon DSLR" -- should command a higher re-sale price when you decide to sell. Of course, you can't go wrong with a Nikon Df if you want a slightly smaller DSLR that looks like an old Nikon F film camera and has lots of knobs! Good luck and have fun shopping and shooting!

I purchased my first Nikon Df in late 2014, and have since acquired numerous lenses, largely based upon YouTube recommendations from The Angry Photographer. Probably the best 100mm lens I have is the 105mm f/2D AF DC-Nikkor, which in addition to being built in Japan like a tank along with a built-in metal lens hood, among other things, delivers unbelievable bokeh. I bought it on eBay for $799. Also recommended is the Tokina 100mm f/2.8 Macro AT-X Pro D, which is great for macro as well as all-around shots. While more "plasticky" and not as solid as the 105mm DC-Nikkor, it's a high quality lens that I purchased new for $369. If you want to have some fun and shoot in manual, I recommend searching eBay and buying a discontinued but minty 105mm f/1.8 Nikkor AI-S. Manufactured in Japan from 1981 through 2005, this lens delivers excellent image quality, rendition and depth. I bought mine on eBay from Japan, and it cost $380 and took about 5 days to deliver to New York City without any customs duties or taxes. By the way, given the Df's design that's reminiscent of an old Nikon F film camera, the old lenses look great. I also purchased the manual focus Nikkor lens that shot the world's most famous photograph -- "The Afghan Girl" by Steve McCurry -- the Nikkor 105mm f/2.5 AI-S. Here is The Angry Photographer's review of this historic lens, also discontinued and produced from 1981-2005: https://www.youtube.com/watch?v=lVIEYk0FDRA&t=200s. Have fun with your Df and be prepared for the compliments you will receive from people seeing you use it.

I've had good luck purchasing used lenses (Nikkor) from both KEH and UsedPhoto Pro (Roberts Photo).

But when it comes to buying older, discontinued Nikkor lenses, I've also had good experiences purchasing used lenses on eBay from sellers based in Japan. Japanese lens sellers are generally regarded as reliable and trustworthy as they have a reputation for taking good care of their lenses coupled with their sense of national pride in selling lenses made in Japan. Their prices also tend to be very fair compared to US-based sellers' prices. I've never had to pay any taxes or customs duties on imports from Japan, and shipping is relatively quick... usually takes 3 to 5 days to New York.

If you decide to purchase from a Japanese eBay seller, make sure they have at least a 98.5% favorable eBay customer rating, carefully read their descriptions of the lens conditions, look at their photos, as well as read some of their recent customer reviews.

Good luck with your lens shopping and purchase.