if the tune up was recent then no need for fuel filter or plugs if you havent yet then you prob should replace sometime after seafoaming. and yes it thins the oil out. you wouldnt want to take any chances
As far as leaving it in the case, I was referring to what others here have done--Search it and you'll find many threads on seafoam. Also if you google it, there are a few seafoam vids on u-tube, one or two by camry members here.