Everything is dependent on where the main line is in relation to the new fixtures. If the main line is directly below the desired water closet position, more of the floor will need to be removed to place an offset in the line. There must be a vent between the fixture trap and it's connection to the main line.
If you were to pick 3 plumbers, each of them would do it a little differently. The best thing to do with whoever you choose is to insist that a permit and inspection be done through the munipality to help ensure that the work being done meets the applicable codes. Anyone who refuses to pull a permit is trying to circumvent doing the job right.