Port your number to Google Voice so you can call/text (and be called/texted from) the U.S. for free anywhere you have an internet connection. Set up Whatsapp and/or the messaging app of choice where you're going to use your GV number so you don't have to mess around changing it. GV's call quality isn't as good as VoLTE, but it's just as good as pre-VoLTE cellphones as long as you have a solid internet connection.

Don't bother paying for American cell service if you're not in the U.S., just get a prepaid SIM or eSIM in each country you go to. Other than Canada, Central Asia ("the Stans") and the least-developed parts of sub-Saharan Africa, mobile data is cheaper in most places than it is in the U.S., and I suspect you'll be finding places to stay with good wifi for your computer anyway.

If you're planning to come back to the U.S. for a few weeks/months at a time, just get whatever prepaid plan suits you best (IMO that's often Mint or T-Mobile Connect if T-Mo's network serves your needs and Visible if it doesn't, but your needs may vary). Leave your number with Google Voice and just treat your new carrier number as a throwaway. For really short trips, I just use a cheap data eSIM.