Computations in toroidal geometry are systematically performed for the plasma response to 3D magnetic perturbations, produced by ferritic inserts (FIs) and test blanket modules (TBMs), for four ITER plasma scenarios: the 15MA baseline, the 12.5MA hybrid, the 9MA steady state, and the 7.5MA half-field Helium plasma. Due to broad toroidal spectrum of the FI and TBM fields, the plasma response for all the n=1-6 field components are computed and compared. The plasma response is found to be weak for the high- n ( n > 4) components. The response is globally not sensitive to the toroidal plasma flow speed, as long as the latter is not reduced by an order of magnitude. This is essentially due to the strong screening effect occuring at a finite flow as predicted for ITER plasmas. The ITER error field correction coils (EFCC) are used to compensate the n = 1 field errors produced by FIs and TBMs for the baseline scenario, for the purpose of avoiding the mode locking. It is found that the middle row of EFCC, with a suitable toroidal phase for the coil current, can provide the best correction of these field errors, according to various optimization criteria. On the other hand, even without correction, it is predicted that these n = 1 field errors do not cause substantial flow damping for the 15MA baseline scenario.