Whether you get a same-day Oath Ceremony or not depends on your particular field office and it can even be a "day by day" thing too. Some field offices do same-day Oaths all the time, others (like mine in Los Angeles) did not do it when I had my oath during the pandemic. However, L.A. had oath ceremonies every Tuesday, so if you had your interview early enough on a Tuesday, there was time for them to get your certificate ready and you could attend your oath ceremony that same Tuesday, later in the day. So again, it differs a lot, even within the same field office.
If you have a name change, some field offices require you to take your oath in front of a judge, which can take months as courts don't have time doing this all the time.
My field office in L.A. did not have a judge present and we did our oath outside the USCIS building. So not all field offices require a "judicial ceremony" when you change your name. You just get your name change document (signed by a judge) in hand together with your certificate at the end, when you hand in your greencard.
You are a greencard holder until you take the oath. That means you are still a greencard holder even after you pass the interview, so you can keep traveling with your greencard even after the interview, until you take the oath.
If you cannot get a US passport in time for your travel, you can let the IO know at the interview which date you will be back in the US and they won't schedule your oath until then. Many have been successful with this, however, it's still USCIS and anything can happen. Personally I would not let anything get in the way of me becoming a citizen and get my US passport, especially not something as unimportant as "travel". Once the citizenship and passport part is done, you're DONE with USCIS and can do whatever you like, including travel without restrictions.