I think I've got it now

What I had:

(C:) SAMSUNG 980 SSD 500GB      PCle 3.0x4, NVMe M.2 2280   10.21   7.22

(D:) ST1000DM010-2EP102 Seagate Barracuda 1TB 7200RPM SATA HDD

(E:)  CD/DVD optical drive SATA

(F:) Crucial MX500 1TB 3D NAND SATA 2.5 Inch Internal SSD  9.2020

(S:) ADATA Swordfish 1TB 3D NAND PCIe Gen3x4 NVMe M.2 2280 Read  9.2020

(with S:) QNINE NVME PCIe Adapter, M.2 PCIe NVMe SSD M Key to PCI Express 3.0 x2 Expansion Card with Low Profile Bracket for PC Desktop

I proceeded to add a 2TB Crucial SATA Internal SSD, used Macrium to clone the existing F: drive (the main data drive) to it, then Disk Management to expand the volume to make the entire 2TB accessible.  Then I changed the drive letter so the 2TB is now the F: drive.  

The power cable in the 2.5" slot had two inputs, but not two data cables, so I ordered one.  That arrived today, and I installed it without any issues.  

What I have now:

(C:) SAMSUNG 980 SSD 500GB      PCle 3.0x4, NVMe M.2 2280   10.21   7.22

(D:) ST1000DM010-2EP102 Seagate Barracuda 1TB 7200RPM SATA HDD

(E:)  CD/DVD optical drive SATA

(F:) Crucial MX500 2TB 3D NAND SATA 2.5 Inch Internal SSD  9.2020

(G:) Crucial MX500 1TB 3D NAND SATA 2.5 Inch Internal SSD  9.2020

Missing:

(S:) ADATA Swordfish 1TB 3D NAND PCIe Gen3x4 NVMe M.2 2280 Read  9.2020

What I learned:  on the motherboard there are four SATA ports.  If there are fewer than four SATA drives, the NVME PCIe adapter will allow a stick SSD to use one of the ports.  When I added the fourth SATA, there was no more room for the adapter.  

Now the D: drive will be an onboard backup for everything on F: except the photos, which will go on G:.  There will continue to be multiple external backups, one of which will remain offsite.

One source of info, from Reddit, and another one, this one from Dell, Quote: "It has 4 sata ports (one blue two black one white).  If you have an optional ODD, then there are three left for HDD/SSD.  If no ODD, then 4 HDD/SSD max.

"note the white sata port is reserved for optional odd, but there is nothing stopping you from giving up odd and using the port for hdd/ssd.  as far as mobo is concerned, it does not matter whether it is odd or ssd.

"its 2.5 bay can accommodate two 2.5 hdd/ssd"

Voices of Experience

 * Jack Benny, who built a career on kidding about his stinginess, his constant age of 39 years and his old Maxwell, doesn't look even near his real age, 80 years. "I don't feel my age," he said, and added a quick aside. "There are moments, of course."

"I think the secret of staying young is to keep working until you can't."

* As far as 67-year-old Robert Young is concerned, "Real fulfillment is knowing what you want to do — and being allowed to do it. ... I want to work 'till I die." He says this after having tested retirement for six years...

"There were some of the unhappiest men in that retirement community," he reveals. "Former chairmen of the board — some who had ruled business empires. I'll never forget the day one of them complained, 'I woke up this morning and thought, what in the hell do I do today?'"

* Larry Brown said, “I think we’re all wired the same. We need to be busy. We need to be active. You need to feel like we’ve got a purpose and a place. Relaxation and time off gets the better of all of us. I’m at my worst when I have time off.”

* Sergio Aragonés draws regularly, basking in each day at the table: “Your only fear is that with age, your hand or brain will fail. So far, I’m 85 and I’m still okay: The brain is still thinking and the hand is not trembling.”

https://www.nytimes.com/2019/06/20/sports/julia-hawkins-running.html

Do you have any secrets to longevity and staying in shape?

To stay in shape, just keep active. Keep your weight down and exercise. Have a lot of passions, things that you are interested in. Keep interested in a lot of things to keep you busy and keep your mind busy.

And look for magic moments. That is something that I have done in my life — think of the things that are magic moments that happen to you, like sunsets and sunrises, rainbows, beautiful birds, music and people’s lovely comments to you. All of those are magic moments and they are free for all. Be sure to keep your eyes open for them.