The fear of committing to a monastic lifestyle
By practicing monastic life, if you mean becoming a monk, it's a no go with your current condition. But if you just want to practice meditation, staying at a monastery, you still have to give up Marijuana and Nicotine. No serious monastery would allow you to smoke while you stay there. 

Some monasteries allow lay practitioners to take just 5 precepts and have food in the evening as well. But usually you have to bring your own food for evening meals.

I would suggest for you to do an online meditation course and to get advice on how to give up your addictions while consulting a doctor to treat your ailments without Marijuana and Nicotine.