Check out ServeTheHome's "Project TinyMiniMicro" on Youtube for a great overview of ultra-small form factor ("1 liter") business PCs.
The big three PC makers each have standardized products in this form factor with (relatively speaking, compared to smaller manufacturers) tons of spare parts available.
Just get a used ultra-small form factor PC a la the Tiny, Mini, or Micro series. A higher-end one which is 7 generations old will still absolutely destroy the Pi in terms of performance.
Once I gave up (for now) on doing all this on ARM and switched back to x86, everything got way easier to actually accomplish.