Let me reassure you that waiting months to treat MAC is not always bad, and it is far better to start with a good plan than it is to start with the antibiotics and wreak havoc with your other conditions.

My MAC went untreated for many months after it was discovered because I had another infection to clear first. I also probably had it for at least 2-3 years before it was discovered, repeatedly being treated for asthma & bronchitis without improving. Yours is a typical story for many members of our group - "accidental" discovery while being treated for something else.

Nodules and ground glass opacities plus a positive specimen are not, by themselves, sufficient reason to begin treatment. Unless you are experiencing relatively severe symptoms like frequent coughing, bringing up a lot of mucus, and fever, you probably have a chronic infection, not an acute one.

There is a complex protocol that surrounds making this decision. You can read about it here:
https://www.ntminfo.org/wp-content/uploads/2019/09/Guide-for-Patients-with-NTM-Infections-2019-09.pdf
I would suggest paying close attention to pages 9 & 11 - making the decision whether to use antibiotics or "watchful waiting" We have members who have been doing exactly that for years.

Waiting 3 weeks to see the pulmonologist seems prudent to me. At the same time, maybe you can arrange consults with your other doctors to get their input.

Finally, did the ID doc give you any indication as to how many colonies of bacteria grew from the culture? This is another indicator that goes into the decision whether to treat.

(PS I know 2 people who have the same "accidental" diagnosis as you, are asymptomatic, and have other health issues. They will not start antibiotics until they are symptomatic or their CT scan shows the infection is progressing - which may be in years, or it may be never.)