Consider running the 32 bit ones under Parallels.

I seem to recall reading somewhere that recent Mac OSs can work with external DVD devices but not for some reason with their own Superdrives.

Take a look at PhotoMgrPro in the iPad App store.

I have scanned photos into .jpg, .tif, and .dng on my Mac with Vuescan and found that the images do in fact look different to start with. I set the file extension to be the same as the file type (.dng for DNG, .tif for TIFF) to make it easier to differentiate them (I have set the computer to always show file extensions.). I also set the DNG parameters to 64 bit. Playing around with the files, some formats seem more suited to certain types of photos than others. You seem to have named your DNG scans as .tif files and the TIFF scans as .dng files, so you may want to check that.

You can find DVD recorders used on ebay for under $50 that will do the job.

I had a very nice print from artbeat studios a few months ago.

Did you reboot? Solves a lot of odd problems.

Imazing is a good idea, as is using Image Capture, a very useful and underappreciated program available on every Mac. I personally use Image Capture.

I have a cheaper Asus second monitor for my 2018 iMac, and it often takes 2-3 seconds to come on after a wakeup call, so some delay is to be expected, but not minutes or hours.

I've used Scanner Pro for a few years and found it very good.

I had no problems at all with installing CS6 on Sierra from Time Machine. I doubt that you will either.

Large volume processors used tanks with nitrogen burst to avoid having multiple people employed agitating the film every minute.

I would assume the data sheet time is for a tank. I personally would try one shot developed at 6.5 minutes and see how the contrast looks. If you print on VC paper the adjustment would not be too hard to make, and you would know what to use for the second development time.

It looks as though the date is the date it was scanned by the Nikon Coolscan. Try using ShootShifter, which I believe is available in the App store. It is well worth the price and can solve your problem. Or, perhaps use a Keyword which is a date or year, and then have Photos sort the images by years.

I've used the Super Coolscan 4000 with VueScan for probably the same number of slides as you have and had minimal problems. The feeder does sometimes not load the slide if the mount is a bit warped, but a credit-card size piece of plastic which narrows the vertical gap on the SF-200 feeder can be a great help. I do like to be next to the computer while it is scanning so that I can quickly catch any hangups, though. I just work on other projects or simply read a book and listen for any unusual loading sound. It also helps to be there as one can put 20-30 slides in at time, and replenish the supply as they get scanned, thus minimizing the time for the whole process. You may find the loader consistently loads the slides at a slight angle, so a bit of experimentation and adjusting VueScan to change the angle will be a great help, as will scanning some of the mount and cropping it later (I use Photoshop). I have set VueScan to automatically save the preview image to speed things along, too. Also note that different brands of slide mounts have ever so slightly different apertures, and this method will help with that problem if you want the absolute maximum image. BTW, I am connecting to a newer iMac with a couple of adapter cables with no problems.