im sure its safe to run your car down until the light comes on. im sure the wonderul people at toyota have designed the tank to hold extra past what the indicator shows just so you cant run dry. i run my tank down to the last indicator or none at all all the time. i fuel up asap when no lights are up because i would had to be sitting on the side of the road with 4 ways on. but like on my friends saturn when his tank was on "E" it still had two gallons left in the tank
Right in my manual the wonderful people at toyota say not to run the car below 1/4 tank. Right there in black and white.
As for how far you can go... no idea.. wouldn't want to try, my brother's a mechanic and would kick my ass if he saw me doing that.