A Uno has plenty of pins to handle the requirements but it is large and clumsy/insecure to connect to. Consider using a smaller board such as a Nano and soldering the connections to it.
A car is a noisy electrical environment and as such is not ideal to provide power to a microprocessor so keeping the power supply clean should be a consideration
As far as I know the MQ-7 sensors are not in themselves calibrated so you need to decide how you are going to do that