Thank you so much for taking the time to clarify my questions. The information I received here was much more accurate and helpful than what I got from the USCIS chat agent, which only caused confusion.
Here’s how I currently understand my options:
Wait to move to the Philippines (since my husband is retiring in 2 years) and file for the N-600K from there. Once the interview appointment is scheduled, I’d request a visa and bring my son to the USA for the interview. After approval, I can apply for his passport and Social Security number.
File the I-130 as soon as possible, then travel to the Philippines for the interview at the US Embassy. If the IR-2 visa is approved, I can bring my son to the USA. After arrival, I can apply for his US passport. While not required, I could also file for a Green Card and the N-600 as additional proof of citizenship.
For everyone's reference, the USCIS chat agent confirmed that filing the I-130 would result in a Green Card, and that I would have to wait 5 years with the Green Card before becoming eligible for US citizenship.
Thanks
JF