The method allows a pressure test of a string with external packers without having the packer setting apparatus exposed to tubing pressure so that at a later time and at a lower pressure than the pressure test pressure, the external packers can be set with annulus pressure opened to a piston that references a low pressure chamber. The packers can be set in any desired order. Thereafter, a circulation sub can be triggered to open to allow the fracking to start. Fracking each interval beyond the first in an uphole direction can be accomplished with pumping ever increasing balls to seats associated with sliding sleeves to open the sleeves in order. In cemented completions, after a pressure test, a ported sub can open on a timer or other signal to allow pumping a combination of a bridge plug and a perforating gun to the desired location.