The tail rotor does need to have some pitch to counter the 5 deg of pitch in the main blades during hover. You should lengthen or shorten the rod or move the servo to get both the servo horn and the pitch lever 90 deg to the boom when the sub trim and regular trim are 0. Yes use subtrim to center the servo horns so they are 90 deg when at 0 pitch. With the C30 non adjustable rods there is not much you can do to level the swashplate however when the servos are at 90 the bell cranks should be at 90 and the swashplate should be level. A slight bit of right is needed to counter the p factor of the head.