Trying to not be too technical, consider what settings you'd like to use for the portraits without a flash. Say you like f/8 at 1/250 and ISO-100.

Your flash should support manual settings. Think of these manual settings as a dimmer switch on the lights. At full-strength, the flash is outputting the maximum light, turned on completely. But, if you adjust the flash output downward, you can dim the output to just the exact amount needed.

Use the suggestion above to practice. You didn't say how you normally shoot. If one of the auto settings like Aperture priority, experiment with two approaches:

1) Set the flash for i-TTL / TTL or similar Auto where the camera and flash sync to each other. Consult your manual and find how to control the 'Flash Compensation'. Using FC, you can dial-up / dial-down the exposure to tell the camera to brighten or darkening the results. I believe the D7200 manual has an entire chapter on 'Flash Photography'.

2) Set the flash to manual and consult the flash manual so you can test / set the 1:1 (100%) output as well as lowering the output down to say 1:64. You can leave the camera in Aperture or whatever setting you prefer. If you tested with FC, set that back to 0 / neutral so the camera just triggers the flash, but doesn't try to control it.

Take a lot of test shots. Review the images on your computer and consider what was 'good' and / or 'bad'. Identify corrective actions, consult the applicable manuals (if needed), and practice again until you can set the camera and flash and achieve the desired result. Using some test shots, even for the actually shoot, is expected to dial-in the exact flash settings.

Well if you are doing this correctly then you should still only end up with 3-4 drives. As you noted the OP is going to a 5 or 6TB drive. In five years time he will transfer all his 5-6TB drives over to the 40TB drives and so on. But you need to get rid of the previous generation of drives otherwise your children will consider you a hoarder.
And I suppose it does matter when you started this. We went from 1 > 2 > 4TB drives and I am fighting my wife to stick with 4TB a while longer. Not so much because I begrudge the cost of moving from 4 > 8TB for example but because our backup (and offsite backup) means another 3 x 8TB (as well as the original) drives plus corresponding longer backup times. We had a big sort out a few days ago and by flattening PSDs (and some other stuff got sorted) she recovered 800GB. So I am stoked with that.
It is hard to tell but most photographers seem to have a period of 20 active years accumulating stuff. My wife has been doing it for well over 20 years although fortunately some of this was film and she doesn't seem to want to scan most of that. Then she got a D850, a friend who is even worse than her, starting to play with video, and being a graphic designer anyway a proclivity to 'play' with Photoshop. It is a constant battle to keep the output down.
Going back 25 years I remember a customer coming in complaining how he had employed someone fulltime to help him write a book. It took 6 months and then the HDD failed and they had no backups. Ever since then I am 'big' on backing up. I would tell a customer 3 times about the importance of backing up. Then I didn't anymore and had no sympathy when they lost stuff

Lots to comment on here -
1. I have made lots of errors using the 'delete' key (erase ?).
2. I generally see older people making less mistakes than younger people. My favourite expression is 'a 26 year university graduate with no life experience'.
3. I am not swimming in the apple world. I don't even like apple stuff or the company attitudes. Since I was 28 I have been in the computer industry working for others and then myself. Even before I started in the industry I repaired analog computers. I have seen it all.
4. My backup programs, when interrupted for any reason, pick up where they stopped.
5. If you make errors so serious that you are screwed then you are operating beyond your area of competence and should even be using a computer. Not at this level anyway.
6. Partitioning confines nothing that properly performed backups can't.
7. What the OP is doing will be copying stuff off a selection of smaller drives onto a big drive. The copy process will stream this data so there will be little excessive head movement. If this is being done as a backup, and my experience of backups is the data is little, if ever, accessed again. And the data copying is best done by a backup program which has shown itself to be 2-3 times faster than explorer.
8. If the OP wants to start serious editing of data on the big drive then he/she needs to make sure the big drive is seriously under used because otherwise editing will soon cause out of disk errors.

If the OP wants to really get serious with the idea of backup then he needs 3 x big drives. Then he will have 2 copies (plus the original disks) and one spare drive. Now every 6 months you copy one of the drives to the blank drive. Then repeat. Why ? Because the best way to find a faulty drive is to actually use it to copy large volumes of data. Media errors etc show up that wouldn't be obvious otherwise.

You can get errors in the directories which might make access bad. Equally in the early days I saw so many times when the partitioning tables went bad and you were equally screwed. I still fail to see how partitioning will make it easier for old people only.

I just bought a 5 Tb external hard drive for the purpose of dupping from other old hard drives so that 'age' and advanced technology doesn't interfere with keeping those images.
Next week I will start and I'm hoping that as I transfer each H.D. icon onto the new H.D., that each old H.D. will stay independent. My expectation is to see 6 different icons on the first page of opening the new H.D.

I have never tried this before. Over time I kept buying a newer backup drive.
When searching for an old photo, rather than attaching every h.d. independently looking for an image, they will all be on one drive.

Do you guys think my logic right ?

PS: I do not like the cloud stuff. I've heard so many people complaining that loading up is OK, but downloading back to your computer is a pain, a long time pain.

I don't remember where precisely, but I've read recently that the use of micro SD cards with the adapter are not recommended by several camera manufacturers as well as photographers and have to wonder why. I guess they do have a second set of contacts that could cause issues, but I've used them almost exclusively for years now and have not had any real issues. In fact, the one SD failure I did have was on a full sized card and I think that I may have caused it by accidentally turning off the camera while it as writing to the card.

In any case, I would be very interested in hearing of any problems others have encountered with the use of the micro cards with adapter in any sort of photographic endeavor. Thanks for your input in advance and good luck and good shooting to all.