Electronic – Is this circuit an instrumentational amplifier? Is there an error in the circuit

A instrumentation amplifier is more than just a opamp hooked up as a differential amplifier. The inamp puts buffers in front of each of the diff amp inputs. This presents a high impedance to the outside, and also eliminates the cross impedance between the inputs of a bare diff amp.

In theory you could make a inamp with three opamps, but in practise that still won't be as good. A real inamp benefits from all the components being on a single die, which help in matching thermal characteristics and ballancing the gain of each input to get better common mode rejection. Precision inamps go thru a laser trimming process in production to get the absolute and relative gains just right.

1. You can use any amplifier you like. You will get better performance if you use a modern $5 dual op-amp than a 2-cent/amplifier LM324. Sub-zero means nothing to me. If you want to the amplifier to have guaranteed characteristics below 0°C, then you should buy one that is guaranteed for that temperature range. Below -55°C you may have to qualify them yourselves. For temperatures down to -20°C it's unlikely that anything untoward will occur other than possibly slightly worse performance for a chip guaranteed over the commercial temperature range. A single 5V supply will impose significant limitations on the input common mode voltage. You can add pullup resistors to the output of an LM324 to get a bit more range (you probably do not want to do this on the output amplifier). Note that the left two amplifiers can saturate at either rail, so even if the output should be within range that doesn't mean that the amplifier will work properly. I presume your common mode input voltage will be close to 2.5V so this may not be a problem. LM158 and LM124 ancient designs are particularly crappy amplifiers for low level DC- large offset voltage and large offset drift with temperature.

2. See above. Offset voltage, offset voltage drift. Probably useful range of input. Closed loop gain accuracy will likely be lower too, because of op-amp gain.

3. If you could use an analog switch with your micro to auto-zero the amplifier you could improve performance. A SPDT switch is sufficient (eg. 1/2 74HC4066). Just transfer one input to be shorted to the other at ~2.5V and measure the amplified offset voltage. Average over many measurements and subtract from the measured signal.