Industry standard is (and has been for years) that the low fuel light will come on with approximately 10% of the capacity of the tank left in it. If you have a 16 gallon tank, there will be roughly 1.6 gallons left when the light comes on. However, measuring the fuel level in a sloshing tank is not an exact science.
As for the fuel pump issue, it's a non-issue... urban legend. The pump is always running, fuel is always being dumped back into the in-tank reservoir through the return line, the pump is always immersed in fuel, and there is always fuel flowing through it, and any debris in the tank gets caught by the pre-filter long before it gets to the pump. I've been happily and confidently running my tank to the light since new with 128k on the odometer. I used to assemble the tanks in the plant in Dearborn... I'm not worried. (Heck, now that I think about it, I probably assembled the tanks in a few member's vehicles on this board LOL!)
-Joe