Someone else who I haven't spoken to since the early days of Creative Image Maker! Trust you keeping well too.
The arthritis thing, although not currently relevant to me, is important to me. Why struggle with something, when proper design can help! So, I've got a couple of designs in my head to help alleviate the issue of tensioning the rear panels.
Funnily enough, I will be starting with glass plates in the new year so it's interesting to see you write about the sizes needed. If I understand you correctly, you do not need a glass front fitted to the frame, as that will be accomplished by the actual plate itself.
Not having a 4x5, is the glass size actually 4" x 5", or is slightly different?