i'm near an international airport that isn't all too busy wiht jet traffic. it has a mix of mostly turbo props and 737s alike. the overhead enroute traffic peaks at certain times of the day that doesn't typically coincide with the terminal rush.
will one scanner do the job?
I'ld try one scanner first and see which positions you can receive (tower, ground, approach, departures) and whether you can receive both sides of the communication. Planes in the air generally pose no problems and if there are no big obstacles (hills) between you and the airport transmitter antennas, you should have ATC crisp and clear. Planes on the ground can be more difficult. Try what works on your location, it's likely that you'll get something interesting on the airport frequencies.
For enroute traffic, you'll likely get the planes. Whether you'll get the controller depends on where the center transmitters are located. If you're lucky there you can set up a second scanner with a few sectors of enroute traffic.