Need some help getting to the airport from Bacharach

The simplest thing to do would be to take the RE2 train. it's direct from Bacharach to the Frankfurt airport. I'd highly recommend taking the one at 1736 but there's another at 1936. Those are the last two. If you don't like that you can get a later train, but they require changes, and you take the risk of very possibly missing a connection.

The RE2 takes just under an hour.

To make it clear our flight is on Tuesday morning at 10:55. We’re thinking about going the night before but aren’t if it would be better to take a morning train instead

If your flight is direct to North America, you must be at the airport no later than 8:00 am. So you really need to take the 5:37 am RE2, as it is the only direct train that gets you there before 8:00 am. If there is any hiccup in the rail system, and I can think of many possibilities, you miss your flight and things get expensive. Going the night before is the safe choice.

Bacharach is working poorly for your fly-out morning. I would overnight in MAINZ the night prior, as I've often done. After a half day or a full day in Bacharach, cruising, whatever... catch a direct RE2 train to Mainz for the pm (a ride of just 30 minutes.) In the morning, there are 4-5 trains every hour that run directly from Mainz Hbf to FRA airport and take just 20-25 minutes.

Mainz is a nicer place to finish up than the airport. Nice old town zone with adjacentsights/shops/dining. You can wake up in Mainz at a decent hour and maybe even get breakfast there. There's a 7:10 RE 2 train, a 7:32 S-train and a 7:44 RE 2 train as well that will get the job done. Check the DB schedule for your travel date, of course.

Mainz' old-town zone with shops and dining, near the main square and cathedral

If it were me I'd stay the night in an airport hotel the night before. The Hilton and the Hilton Garden Inn are both located in a building that houses the airport long-distance train station and is adjacent to the airport (The Squaire). The whole way is under cover so you just wheel your bags from the train to the hotel to the airport. We have stayed in the Garden Inn which has a breakfast room but no restaurant, but the Hilton proper has a restaurant. There are also food shops and a drugstore (Drogerie, no pharmaceuticals) in the same building. It's all very easy - I would rather do that than risk a problem with the train somewhere on my last morning, and you do have to be up very early to make it to the airport at an appropriate time.

Lavandula

I would want to be closer, the only sure thing we found with German rail, is that the train would be delayed, or service interrupted.

I would find something in the Frankfurt area (I guess we all are assuming you are flying out of Frankfurt, you don't say), make an afternoon of it and a nice evening. I would not stay directly at the airport, Mainz or in Frankfurt would be much better.

I’ve taken the early train 2-3 times with no problems but given the train problems last time in Germany, I think Mainz or Frankfurt is a good idea.