hiphop: Interesting story on your sabbatical. You should consider
returning to Lisbon for a visit.

(1) Taxes: As Manlobbi alluded, aside from Eritrea, the US is the
only country which taxes based on citizenship. It's not so bad,
however, as the US has a reciprocity agreement with Portugal, so taxes
you pay here (if you reside here) will offset what you pay to the US.

(2) Communications: My intermediate solution is a dual-SIM phone
with the US number as my secondary. My Portugal SIM handles voice
and data. I'll eventually retire the US number. For people who
are here short-term, you can pretty much handle most tasks via
WhatsApp.

(3) Bank accounts: It's a hassle as a US citizen opening a
European bank account, but it's doable. I set up my account
remotely before moving to Portugal, which I would advise if
possible. There's also options with Wise and Revolut.

(4) Renting cars: It's pretty easy here and not very expensive,
aside from operating costs (fuel, parking, toll roads). As a
American I was able to exchange my US driver's license for
a Portuguese license (some paperwork and time involved). If
you do this within two years of moving here, you can avoid
taking the Portuguese driving tests. For short-term stays,
your US driver's license will work fine. I should mention
that I don't find it necessary to own a car here, so obtaining
my driver's license was mainly so I can rent a car if I ever
feel the need.