The case is
finished! At some point when I'm not exhausted from working at work and working at home (on the case), I'll post a detailed guide of how I made it.
In the meantime, I put up back panels (plywood covered in contact paper for easy cleaning) + metal mesh for ventilation:
Added IKEA Dioder color-changing LED light strips
Covered cage floors and edges with contact paper as well, as it's so easy to clean.
Had glass cut to size for sliding doors and bedding guards. Had to make my own tracks for the glass to slide in, as it's 1/8" glass, and I couldn't find such skinny tracks in hardware stores (didn't bother looking on-line).
There's still some white protective paper left on the case in these photos. I've since taken it all off.
Now it's time to clean... the apartment. Then I'll put Viola in first--she's going to go into the middle enclosure. Lucy will be in the top one, I think, and Lazy Izzie in the bottom.