How can I determine what the minimum working pressure is for a gas range?
You may not be able to use a 5 gallon (20 lb?) tank as the supply for a range top - effective propane delivery depends on having adequate tank to boil off the required supply of gas - depending on how much the range uses and the temperature, a 5 gallon tank may "freeze up" (really, self-cool) to the point where it does not provide the gas required - a 100-200lb tank is certainly much more standard as the supply for a propane range.

LP stands for Liquified Propane - it has the useful feature for storage and transport of becoming a liquid at relatively low pressures. when you draw gas from the tank, the liquid boils - as it boils, it cools the tank. If the tank is already cold (question is from February) and the gas use rate is high, the pressure in the tank falls to 0 at roughly -40 (F or C) A larger tank has more area to collect heat from so it cools more slowly for the same rate of gas use.

Using the correct regulator (for delivery pressure with adequate tank pressure driving it) is also required...

This previous answer may also shed more light on the subject.

If my regular propane tank for the house runs out, can I use a BBQ tank as a temporary fix?