One would be insects and pests, although your plants are pretty big already u should be able to keep them off if u spot any right away. Pests make seedlings highly vulnerable as they only have a few leaves to be eaten, which is why its good u started indoor. Another thing to keep in mind is the sun and temps. If the temps are different outdoor than in ur grow room, you are going to need to slowly adjust your plants to their new enviorment. Meaning a couple hours a day to start off with, gradually increasing how long they are out there. Other than that, nature should treat you nice, seeing as you seem to know what ur doing