Check in time at Rome airport

2 hours prior to departure will be more than adequate. It's an Intra-Schengen flight, so it works like a domestic flight in the US.

Whether you want to stay at the airport hotel (like Hilton Airport) or in the city center is up to you. If you are at a hotel in the city center of Rome already the nights preceding your departure, I wouldn't bother to change hotels just for the last night. The taxi ride from the city center to the airport is about 30-40 min max at that time in the morning.

Roberto is absolutely correct. Two hours -- it is consider a local flight to Germany. I would stay in Rome and have a great final meal. And that early in the morning should be little pressure on security. Check in and go the gate.

Thank you so much for your reply. Since I've never done this before....flying to Frankfurt from Rome sounds like that check in at Rome airport is easy. We have a 2 hour layover in Frankfurt and would like to use the United lounge or would it be a Lufthansa lounge because they are partners? I read up a little bit about the airport and it looks that we will be arriving in a schengen gate but then have to leave that area to access a non-schengen lounge (Lufthansa or United?).Before boarding the flight to Houston do you then go through passport control and security check? I assume that would have to be in a non-schengen area? I hope that you are someone else in this group has experience with the Frankfurt airport and can help me. Thank you so much for your help.

You'll go through Schengen exit passport control at FRA.

I've flown from Europe to the US via Frankfurt so many times (including twice in the last 15 months) I can't even count.

I've never used the Lufthansa lounge and I don't know if my United Mileage Plus level would allow me to do so. In any case if you only have a 2 hour layover you won't have a lot of time to spare. You will need to change gates from the A-gates to the Z gates (both are in terminal 1, with Z gates one level above A gates) and T1 is rather long, so you might have to walk half a mile or more to make the change (there are walkalators, or moving walkways, but still it could be a long walk). Passport control will be at the Z-gates level as soon as you go up the escalators from level A-gates (the gates at which you disembark from Rome). US bound planes depart from Z gates.

I wrote a reply regarding laying over at FRA in the thread below. Take a read:

https://community.ricksteves.com/travel-forum/italy/flying-to-venice-from-denver-through-germany

It’s been a few years but I used the Lufthansa lounge the last time I connected to a United flight at Frankfurt. I made sure to get through passport control and security to the Z Gate area. Then found the lounge. I appears there are 2 lounges in the Z gate part of the terminal. Select T1 Z gates in the link. Business lounge and a senator lounge. I believe the senator lounge may have more restrictive entry requirements.

https://www.frankfurt-airport.com/en/services/lounges/exclusive-lounges-at-frankfurt-airport.html

Thank you all for your replies! This has been so helpful, I feel much more confident about where I should be going in the Frankfurt airport. Blessings to you all.

Skip the lounge, you don't have time.