The plan seems to be to have the first 2 cargo missions carry robots that can make a concrete landing pad. It isn't really sure if that will work out, however, and I suspect that they aren't going to be able to land that accurately.
As far as the initial landings, I'm sure they will get HiRISE observations to look at the landing ellipse, same as every mission since it arrived on Mars, and make sure it looks clear.
I'm pretty sure that the first two cargo BFRs are never coming back to Earth, and if so, not for some time. The improved landing is probably only required if one intends to reuse the spacecraft, also Mars has less gravity then Earth.