I think your burden resistor is a little high. When you subtract allowances for component tolerances etc from the 3.3 V peak to peak, I get 1.1 V rms as the value to design for. That gives me 41.26 Ω, so I would go with 39 Ω, giving you a little over 210 A maximum current. With your 43 Ω burden, I could not guarantee undistorted readings from a pure sine wave above 192 A. If that’s OK with you, fine.
Not really. You want them on a circuit where there are no large loads and as close as possible, so that there is minimum voltage drop in the cable between the bus bars and the ac adapter.
If you don’t have a programmer, you might want one to reload the sketch after you’ve changed the calibration values, which will be wrong because you’re using a different CT and burden. Alternatively, you can calibrate in emonhub.conf (local emoncms) or put a multiplier in the processing chain in emoncms.org.