"Facts" like if you will stop lifting your muscle tissue will turn into fat and on
the contrary that if you start lifting you should first gain some fat so it would later turn into muscle tissue. If you gain fat when you stop lifting it is because you lose muscle due to the fact your body is not under stress (by lifting) anymore. If you lose muscle you burn less energy/calories and you quickly excess your daily calorie intake which leads to obesity. If you eat the same number of calories you must be very careful about your diet.
This is a myth, biologically the statement that muscle turns into fat or the other way around is not correct. Steroids have nothing to do here.
The only reason obese people gain muscle quicker is because of their metabolism and overall weight. Also a very small portion comes from joints which are better developed for heavy muscles so your body can adjusts quicker to the new muscle mass.
If you stop doing sports due to the injury you need to make some changes to your diet as well or you may end up eating too much calories and gain weight. Lower your protein intake to around 1g per kilogram of persons weight. Also watch over carbon hydrates which can easily be exceeded with low GI. When you stop doing sports body stops developing some hormones which can lead up to mild depression which can take its toll and makes the overeating problem even worse.