Re: Shaded panel wiring.
My opinion, which no doubt someone will disagree with in whole or in part:
No need for blocking diodes on shaded panels unless you have very high array Voltage (the other panels will not produce enough Voltage to reverse current flow through the shaded ones).
MPPT controllers don't have a problem with shaded panels any more than PWM controllers do.
Why would you want to switch the Ammeter off? It won't hurt anything to leave it connected providing it is wired right. Where were you planning on installing this? A good charge controller will measure the current going in and out of it anyway, so an additional meter would be redundant.
If you do this, bypassing the shunt through shorting is unnecessary; simply open the lead to the meter so that it doesn't read. If you were to short the shunt the switch would indeed have to be able to take full current and the maximum DC (I assume) Voltage. I just don't see any reason to do this.
Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.
Ohm's Law: Amps = Volts / Ohms
Power Formula: Watts = Volts * Amps