We didn't have a credit check either. Our income had to be at least 25% above poverty level for the size of our family. For a family size of 8, the minimum is $40,487/yearly (except for Hawaii and Alaska). Of course that will be lower if 2 of your children have moved out.
Our homestudy agency and placement agency made us do an income to debt ratio as well to make sure we could afford a child with our lifestyle. We just needed an employment letter from dh's employer stating how long he has been employed, how much he makes, and what he does. I've heard of some agencies asking for bank letters though.
As far as the health issues, our agency and social worker were VERY laid back about this. Both our SW and agency just wanted the doctor to write something saying we were expected to life a normal life's expectancy, that we were physically and psychologically capable of parenting a child, and that we were free of communicable diseases.
Guatemala has no weight requirement, however I've heard of a couple other countries having one. I think it's no more than 20% overweight. I remember looking at it when we were picking our country and noticing that dh was considered overweight by that method. He really isn't considered overweight by American standards at all. I cannot remember what weight it said he had to be, but I'm thinking it was like 175 or 180 which would make him super skinny for his height!