To answer your first question Why I need other pairs? throughout the year we cant expect deviations to occur between the stocks in the pairs. so if we have more reliable pairs then will have more trades per year. thats it.
regarding my strategy. this is the tool i use.
it is based on the mostly used SD2.5 strategy. when the short term deviation between two scrips goes above 2.5 we have to initiate and closed down the position when the deviation revert back to 1.5. this is the conservative method that i follow. some traders wait till 1.0 to 0.5 for bigger profit. 2.5/1.5 is the time tested range.