1a) red blood cells carry oxygen. so if you have more, it means your aerobic respiration will improve.
2) addiction, or they may clash with other medication
3a) it could be bad for the company as their drug is being used for bad, which may encourage others too. a good thing is that it can be easily spotted.
3b) their other medication may not show up, so in an emergancy, medication could be given, but it wouldnt respond due to other medication clashing.
3c) it would be good for athletes as they wouldnt get called out for using PEDs, however it is still a drug.
4) overall, i dont believe markers is a good idea. this is becuase even though it will be used for good, it will be bought under drugs on which people misuse for the wrong reasons. meaning that people may get adfdicted and the drugs doesnt become efficent anymore.
i tried, sorry