1.
If the data acquisition devices have one A/D converter, that need to be multiplexed to the two channels. In other words, each input channel will be sampled sequentially . Therefore, if you use two channels, those channels cannot be sampled simultaneously and a time gap exists between consecutive sampled channels. This time gap is called the channel skew. You can think of the channel skew as the time it takes the analog input subsystem to sample a single channel. In practice, the sampling rate depends on several characteristics of the analog input subsystem including the settling time and the gain, as well as the channel skew. If you cannot tolerate channel skew in your application, you must use hardware that allows simultaneous sampling of all channels.
2.
That’s a normal situation at 5 Amps on a 0.1 shunt resistor, as the peak power P = RI2 = ~ 2.5W.
You need to lower this value of the shunt resistor to 0.01 ohms in order to minimize dissipated power up to 0.25W. But as the voltage drop across the shunt is proportional to the current flowing through it and since its resistance diminish we need to compensate using an additional amplifier circuit. (Amplifier gain= 10)