Decided that the best bet – from a backup point of view – would be to store the data files such as photos, videos and documents externally (rather than in Media), and to keep the WordPress installation light so that it would back up easily.
Successfully trialled external photos, presented using a table layout. Altenate rows are photo, and label (with a white background). You need a blank header row to get the white background on the right rows. This presents well on phone and tablet as well.
It’s essential to have the right file permissions for this to work (755 on the folder, 644 on the files – may need to review the “Execute” permissions)
The experiments at http://www.paulhulbert.org/swehs/bath-test-photos-6/ were with fairly small files, 135 kb (900 x 600 px) to 2 Mb (3304 x 2397 px). An “average” one would be 740 kb (1632 x 1172). Need to consider resizing to a standard size. The photos are presented as 300 px wide, so resizing all to say 1500 px wide would be a good compromise – need to try using bulk resizing in Photoshop Elements, see https://digital-photography-school.com/batch-processing-in-photoshop-elements/
Followed this procedure, selecting 1500 px, Constrain Proportions, and 72 dpi, convert files to jpg Medium Quality. The result was 103 kb to 503 kb, all 1500 px wide. Worked well. Uploaded to replace files, and the page loads quickly. Quite good quality even when clicked on to magnify.