Does the standard A1200 motherboard '020 have a MMU?
No.
I understand it's the 68EC020 so does this mean no MMU or no FPU - or neither?
No. For 68020 EC means it has 24bit address bus, not 32bit. No 68020 model has built-in MMU or FPU.
Why did Amigas never implement parity or ECC like in Unix servers?
Because parity/ECC memory was (and is) expensive and not needed for games machine.
