You seem to have several problems.
Hello
How does low iron levels affect strength gains for starting strength? I have a genetic disorder and due to that my iron levels are just barely at minimum (and sometimes below minimum) if I eat what I normally eat without working out.
I am 6'1" and 140 lb and quite thin in terms of muscle mass (think skin and bones) and thin boned. Should I take a iron pills? I used to do that but I don't anymore since I don't like to stick to a schedule with pills. (they also turn my stool black, not sure if that is healthy for the long term). I also have a cast iron pan that I can use, but I don't typically use it because the non-stick pan is much more convenient.
I plan to eat chicken+ rice+ kidney beans + onions daily to try and get my weight up. (I can't do GOMAD since I can only drink 1 cup of milk a day before I get gas).
Is this a good plan to help get my iron levels up? Do I need to get my iron levels up? I am not sure if I should ask a doctor all of this, but it seems this is the best place to ask about starting strength.
You seem to have several problems.
This is a problem for your doctor to help you get sorted.
THIS is a problem for you to solve with food and lifting iron.
Iron pills do that; it's perfectly normal. Whether you should be taking them is (you guessed it!) a matter for your doctor to answer.
As far as cast iron pans, I've found using bacon fat work very well with them, and will add more calories as well, something you need to get your weight up.
It would appear you don't know how to properly use a cast iron pan, if this is your reasoning for not using it. My cast iron cookware drastically outperforms any non-stick cookware I have. It takes very little effort to maintain your cast iron cookware, other than making sure to keep it coated in cooking oil after every use.
Lodge has a whole line of pre-seasoned cast iron pans, skillets, and pots. Learn how to use them to cook yourself MORE FOOD THAN YOU'RE EATING NOW.