Say you are sideslipping so you have a clear view of the runway thru the pilot side window. You turn the yoke left, so left aileron up/right aileron down, that would start a left banked turn. Then you kick in right rudder to force the tail to move left and counter the left turn of the ailerons.  I do that all the time in my 177, it's a fun way to lose some altitude quick when you realize you're too high on final and don't want to float way down a short runway.

The amount of sideslip that results will depend on how much aileron and how much rudder is used.

Amount of aileroninput depends on the amount of slip desired. Straighten the ailerons and rudder and the plane straightens out. So yes, it must be maintained.