Hi,
Maybe, keep things simple: e.g. 10mV in reads as 10 or 0010 or 10.00, etc., out on the LCD display. Not up on Arduino workings, sorry, anyway. If an ADC has an input range of 200mV or 2V, for example, that would display at most 1999 on a 3 and a 1/2 digit display, so if current range/sensor voltage were 0 to 50mV, you'd need a gain of 4 to make the most of the ADC/display, so long as you take into account the min and max current to be sensed. If the sensor has a min output/offset of midsupply, then you need to bias the op amp to the same level so its output looks like 0A at 0A current. 0mV to 250mV for a 200mV ADC, need to put a divider on the input, that divides the sensor voltage down to 0.8, e.g. 2K4 and 9K6, to fit the ADC input range, then you wouldn't need an op amp to amplify, unless you wanted to add one as a unity gain buffer.
As you know the numbers/supply and device and sensed voltages and currents involved, it's not so hard fitting them together, and reducing them to ratios first to see how they need to fit together for 10mV to look like 1.000A on the LCD. Hope that helps a bit.