How we do this:
- Start with an official stock ZX Spectrum from the commercial era. Any Sinclair or Amstrad-owning-Sinclair model. That means no clones, no SAM Coupe or Sinclair Next.
- Add as many hardware peripherals (joystick, multiface, printer, monitor, whatever) to it but they must have been released in the commercial era AND everything must work with your ZX Spectrum all at once.
- You have unlimited (imaginary) money, so go for it!