The pad on the mic would be between the capsule and the valve, to stop the valve going into mild overdrive if you're recording a loud source you want to keep clean, rather than let the valve drive a bit to add some valve 'character'.

The pad on the interface obviously reduces the signal level into the preamp stage to stop the A/D converter being overloaded, but can't prevent the mic from sending an overdriven signal.

These mics can be made to sound very good (they'll sound good anyway), but as they say, you'll need to swap out most of the provided components for more upmarket devices - especially the transformer and probably the capsule.

Capacitor C4 is the one that needs the most care in installing as it needs to be well insulated from ground. That's why it's provided with ceramic insulators for the leads, to keep the body away from the board.