Drain and refill of the trans fluid is an excellent idea for regualar maintenance even if it is not in the scheduled maintenance. The drain plug washer is the same one as used on the Protege engine oil and trans oil drain plugswith OE part number 9956-41-400. Dealer price is 0.90.
Approx 3 qts is a normal drain and fill. I always drain into a drain pan, then pour into an old gallon jug that has been pre-marked at 1 qt intervals, then just refill the amount you drained out. If level was good when you started it will be the same when you finish using this method.
Would not use mobile synthetic if you are just doing a drain and fill as you are only draining out 3 qts or so of a 7.6 qt system. 1/2 and 1/2 not a good thing. Mercon V ATF is specified for your transmission fluid.
Would not even worry about replacing the filter screen untill at least the 30k mark if not further.