If it has 4 wheel disc brakes than it is possible for a 4 wheel brake job at the same time. If it has rear drum brakes then you can "usually" go through 2, sometimes 3 sets of front brakes before you need back brakes.
Your front brakes do about 80% of your braking and this is why they wear out faster. Unless you have rear disc brakes....The percentage is still the same but the brake calipers and pads are way smaller.
As for your light.
Generally worn out brakes dont make your ABS light come on. There are rules to the exception though. I would say most of the time it is caused by sensors and or harnesses to the sensors.
I was taught a good way to diagnose and usually where sensors fail is when you just start moving in your vehicle. Like out of your driveway, or in a parking lot or a line up. Usually at 3 - 5 MPH. So the next time your light goes out, keep an eye on when it does come back on. It might help the mechanic fix your problem faster and save you money.
Hope this helps somewhat.