The compost mix you might want to wait on until you sort out your watering schedule, because it holds water a bit differently and you still have to get a feel for that by the looks of things. If you use it now, make sure there is plenty of perlite- like 1/3 of the total mix. On the other hand, the plant looks hungry, and the light nutes in compost would be appropriate for a plant of that age. Your call.
And untie that poor thing; it's too young to be into bondage- wait until it is healthy before messing with it. There is a chance that you can block water flow in the tissues with too tight a string. Health first, training after.
It looks a hair better. What is your max/min temperature and what are you using for ventilation?