Minimize need for setting changes when roaming internationally for voice calls and data

I recently enrolled in US Mobile’s Light Speed network unlimited premium plan last week and would like to get better understanding on the appropriate settings to enable data roaming when traveling to international country, specifically India.

My understanding for iPhone is I should enable “Data Roaming” under Cellular Data Options (maybe even ahead of time) and this should really be the only setting change. Is this correct?

Do I need to configure the APN Username/Password settings under Cellular Data? Currently, while in US, username/password settings are all blank for Cellular Data, LTE Setup (optional), MMS, and Personal Hotspot.

If enabling “Data Roaming” is all that needs to be enabled, I’d like to make sure this would work seamlessly if I enable it ahead of time and simply turn OFF airplane mode setting upon arriving into the international country whereby US Mobile carrier connects automatically to the local network carrier of the country based on their agreements. Is this possible?

I’m asking for clarity on this as one of the previous posts on this site mentioned the individual had to reach out to US Mobile support team upon landing in Costa Rica and some APN setting changes were required to allow voice calls/data connection to work successfully.

Thanks in advance.