A short update to this post on the Challenges of Boxmaking:
After asking some others via an amazing Facebook group for advice regarding my hinge troubles, I discovered two key things that made this box a success, finally, a year later:
1) Tin your hinge! I use a large version of what I'm told is called a "Jewelry hinge", one copper rod within three pieces of brass tubing. You can see in this picture how the two end pieces are soldered to the box and the center piece. I was trying to solder the un-tinned hinge onto the box and conceal all the brass coloration. A bit foolish, in hindsight. It works much better, and is infinitely easier, if you tin it beforehand.
2) Use paper strips. I tore three paper strips approximately the width of the brass parts, and bent them around the box/lid as appropriate (so the papers on the outside were bent "above" the hinge, around the lid, to prevent solder from accidentally attaching those hinge segments to both the box and the lid. Likewise the one center strip was wrapped "under" the hinge and around the red glass of the box to ensure solder didn't go there either)
Now I have a completed and functional Midrealm Pale glass box.