Iodine is NOT inherently hard on the kidneys. Iodine may kick a lot of toxins out which GO THROUGH THE KIDNEYS. So you don't want to overload the kidneys with too much outgoing junk.
That's the reason many people use the salt loading protocol, to speed up/lessen detox symptoms.
But you might consider doing the salt loading protocol a week before you start Iodine as a pre-emptive strike to get some of the bromide out. A few of the Iodine doctors recommend the pre-emptive salt load.