If you are doing the standard pan drop, in my experience, the Dodge/Chrysler FWD's take a little over 4 quarts, so get at least fivve. also, make sure you use ATF+4. your stratus may actually specify ATF+3, depending on its age, but ATF+4 is backwards compatable and is a better fluid than its predecessors. basically it has the same friction properties as ATF+3 but it uses a group III base stock so its more stable and lasts longer.
Walmart used to carry Mopar fluid, but no longer. you will find ATF+4 licensed fluids from Valvoline and others, including some house brands. expect to pay $4-6 a quart.