It only takes a quart or so to completely refill the system--the reservoir is small, and the pump is directly over the box so the lines are very short. If you are going to be doing a lot of cleanup work you will need to a bunch of fluid to fill and purge.
The best power steering fluid is the synthetic Valvoline ps fluid. I have only found it reliably at Advance Auto, and rarely find it anywhere else. They sell it by the gallon too, and you will probably need 1-2 gallons depending
You can fill it with Type-F ATF and run it for a bit if you like. It will make noise but it will clean the system pretty well. You'll need to completely drain and refill with real power steering fluid. I believe that some of the recent models specify Mopar ATF as usable fluid but I don't know what those pumps are or the properties of the fluid. Type-F is a detergent hydraulic fluid for old Ford transmissions, newer ATF is more of a lightweight motor oil with some additives, so they are pretty different animals.
Easiest way to drain is to disconnect the low-pressure (rubber) return line that goes from the gear box to the reservoir, and let the fluid drain out of the reservoir. This won't evacuate the box or the pump but most of the fluid will be in the low-pressure side.
