Thanks Neale! Very helpful reply which sadly has left me with a few more questions.

1) If the PSU has overcurrent / short circuit protection do I even need an MCB? It sounded from your explanation like the MCBs wouldn't be much help anyway. It also seems as though the SMPS is the wrong choice but I'll probably just switch it out in V2 of this build, I need to get this build completed ASAP.
2) So a 5a MCB would be enough for the PSU and smaller drivers but what about the larger drivers?
3) Would it be a bad idea to have a fuse at the IEC socket combined with an MCB?

Thanks again for the advice