Multimeter circuit review
A few comments:


The ACS712 current transformer you're using has a max bandwidth of 80kHz, below your desired target of 100kHz.
The ACS712 also has a listed total output error of +/-1.5% at a nominal 25 degrees C; temperature changes makes this worse. If the noise is low enough and you have the equipment to measure the error you might be able account for this in software to get better than 1% accuracy, but I wouldn't expect it to just work.
Same goes for the DUE's ADC accuracy: The SAM3x MCU it uses is specified at +.29%/-1.56%, presumably using the internal reference? It's within a 2% range corresponding to +/-1%, but it's shifted down a bit (again, this could be software calibrated out if you can measure the error).
Even if you have no intention of adding full over-voltage protection present in standard multimeters, I would still add series resistors to the inputs of the INA826 to take advantage of the internal overvoltage protection of the opamp Because Dumb Stuff Happens™ (see Fig. 58)
You might need better bypassing caps, say a 1uF, 100nF, 10nF parallel combo. If you're building a custom PCB I would at least add extra pads for these, then populate them as needed.