I agree with Matt when it comes to Power Supply.
Head to Futurlec
as they have a number of different types of Gas, including Alcohol at very cheap prices. They also stock the other parts you are going to need.
You could use an I2C
A/D (Analogue to Digital Converter
) to end up with a more flexible Sensor. A MAX127
or a PCF8591
are a couple of common possibilities for I.C.'s to use. The MAX127
has a better A/D bit rate of 12 compared with 8 for the PCF8591
: being their accuracy of conversion.