First of all I am referring to meat diet as high fat meat diet where most of the calories come from the fat. This should keep the kidneys healthy as the high protein diet is what causes kidney problems.
I don't know about the flora but many of the all meat dieters eat high meat. High meat is aged meat for some prolonged time. Usually at least for two weeks. This contains plenty of healthy bacteria. Inuits do the same by rotting their fish.
I have not read about the iron, so claims about feeding pathogens comes in surprise. I will check it up but I don't see a danger here. Haven't heard any claims about the iron from other "dieters" who eat all meat. I have read somewhere iron and cancer and iron making cancer grow new blood vessels. But how does the cancer grow if there is no glycose ? Actually cancer degenerates on ketogenic diet ( all meat ).
I understand what you might feel about meat. Best knowledge comes from the personal experience. You said you were largely dependent on carbs when you were younger. Getting used to lower carb from high carb might take time and going all meat at once might cause problems. It's funny but body must be trained to use less glycose and eventually when most of the carbs are cut off, body will make ketones from the fat which will be the main energy source for the body.