train in Germany

• Frankfurt airport (not city) - Bacharach: Local trip (and you can't predict when you will exit the airport) so just by at the ticket machine at Frankfurt airport station.
• Around Bacharach - local day pass, or buy local tickets as needed. Both bought on the day at station.
• Bacharach to Rothenburg ob der Tauber (make sure you use the full name, there are multiple "Rothenburg" in Germany). - Buy discounted ticket in advance from DB website.
• Around Rothenburg ob der Tauber - again local tickets as needed or local one-day pass (Bayern ticket)
• Rothenburg ob der Tauber to Füssen - advance ticket from DB.
• Around Füssen, probably using local buses, just buy tickets as needed.
• Füssen to Munich - could buy in advance. Not sure there is a big saving over buying on the day.
• Around Munich and out to airport - local tickets

DB (German Railways) website: https://www.bahn.com/en/view/index.shtml
You can see from that website the difference (if any) between buying on the day and buying 2-3 months in advance. The DB website does not sell tickets for very local trips (like Munich to the airport), these are regulated by the local transport authority.
I only count 2-3 long runs that would justify buying in advance: Bacharach to Rothenburg ob der Tauber, Rothenburg ob der Tauber to Füssen and possibly Füssen to Munich.

P.S. I just looked up Füssen to Munich (München). It is €23, no discount for advance purchase.
The alternative is a "Bayern ticket" one day pass, which covers all trains and buses in Bavaria, including in Munich.
That costs €25 for 1 person, €32 for 2 people. As you are two, €32 is less than 2x€23, and you get Füssen buses and transpirt in Munich thrown in.
A Bayern Ticket is only valid on regional trains (NOT ICE/IC High Speed trains). You could also use one for Rothenburg ob der Tauber to Füssen, but you would then have to be careful to user regional trains only for the leg to Munich.

"If we have the German Rail pass to use for all our days, is that a less stressful way to explore areas and not feel the stress of worrying about train tickets every time?"

Generally speaking, Yes, it certainly is. It's not just the act of purchasing and the handling of multiple tickets and different types of ticket that can be stressful. It's also that with day passes (the Bayern Ticket for example) there's often a no-travel-before-9-am restriction on weekdays. Also, these day passes as well as the local p2p tickets for regional trains will require you to distinguish between regional and long-distance trains at stations served by both types of train; hop on the long-distance train by mistake, and you'll be facing a fine. You have to understand the geographical limits of your day pass as well. It's not uncommon that someone staying in Bacharach buys a local day pass (Rheinland-Pfalz ticket) for local outings, then attempts to use it to reach Frankfurt (not that far away) or Cologne, both of which lie outside the travel zone for this day pass.

And with the pre-purchased saver fare tickets for your 2-3 longer rides, you are locked into using specific trains at specific times for those journeys - there's no flexibility if you want to get up late one morning and take a later train.

For amateur train riders, the learning curve for tickets and convenience of the rail pass are both significant.

For the 3 longer trips, a 3-days-in-a-month twin pass costs €292 for two adults.

It looks to me like a 5-days-in-30 rail pass might work out well for you - €335 for two (so just €43 additional for the two of you for the two extra days.) You could use it for...

• FRA > Bacharach (+ any additional outing you might do that same day.)

• Bacharach > Rothenburg (stopovers, detours possible)

• Rothenburg > Füssen (stopovers, detours possible)

• Füsssen > Munich (+ maybe some S-Bahn use around Munich the same day)

• Munich > MUC airport

That leaves you with just the Rheinland-Pfalz ticket (or individual p2p tickets) to purchase in Bacharach for your outings there - and then any bus outings you will take from Füssen as well with a Bayern Ticket or individual tickets.

It may still cost you more altogether this way, but that's the price for the hassle-avoidance you enjoy.

If you go with the GRP, the DB ticket agents at FRA airport can sell you the pass AND provide you with direct guidance on using the pass. This seems to me a good advantage for the newbie to Germany.

I don't think very highly of some of your destinations, but I think we've already bored you with that chatter on a separate thread. In any case, a rail pass means you don't have to lock in all your sleep-spots in advance if you wish to make changes to your itinerary. Use those 5 rail pass days on any days you wish.

Your trip is very similar to one that I did two years ago.

I flew into FRA and traveled by train to St. Goar,

After two days in St. Goar, I traveled to the Füssen area for two days. Then I traveled to Lindau for three days.

From Lindau I traveled to Rothenburg for a day, then on to a small town on the Main river for 9 days.

Lastly, I traveled to FRA for the flight back to the US.

So, my trip was pretty similar to your proposed trip. I did the trip entirely by rail, using a local ticket to St. Goar, a Savings Fare ticket to the Füssen area, Bayern tickets to Lindau and Rothenburg, and local tickets back to FRA. The only non-regional train I took was an IC from Bingen Hbf to Ulm. And I compared the cost of my travel to other ways, like a rail passes, and I know I saved money.

In your case, the local metro district, RMV, sells tickets at the Regionalbahnhof at the Frankfurt airport to Bachararch for €12.35/P.

From Bacharach to Rothenburg you can use a Quer-durchs-Land-Ticket, an all day pass for regional trains for €52 for two people. Regional trains will take a little over 5 hours for Bacharach to Rothenburg. You can save some time, maybe an hour, by advance purchasing a Savings Fare ticket for about €30/P, but that will be a train specific ticket, so make sure you can commit.

Both Rothenburg to Füssen and Füssen to Munich should be done with Bayern-Tickets, and Munich to the airport is a local ticket.

All of the tickets, except the Savings Fare tickets, should you choose to use them, are purchase-at-travel-time, "take any train" tickets (essential identical to a rail pass) so there should be no stress of having to make a certain train. If you use the Quer-durchs-Land-Ticket, all your tickets for the four major legs plus one-way on the S-Bahn to the Munich airport will be about $180.

For local, in town trips, rail pass days would be much more expensive than local transportation tickets.

All of the tickets, except the Savings Fare tickets, should you choose
to use them, are purchase-at-travel-time, "take any train" tickets
(essential identical to a rail pass) so there should be no stress of
having to make a certain train.

I think the OP's stress is connected to the ticket purchase process - which, if difficult and too lengthy, could mean... 1.) missing their PLANNED train, and 2.) waiting around for an additional hour for the NEXT train. And of course, re-configuring any subsequent train plans/connections as well.

"Take any train" applies to both the rail pass and the day passes - except that with the day passes, it's really "any REGIONAL train." With a day pass, the newbie must learn and understand which trains are which.

The rail pass OTOH subtracts both issues from the equation (indeed, at additional cost.)

When you travel from Rothenburg to Fussen, consider renting a car and taking the Romantic Road. There are some great towns, villages and cities on the road.
https://www.romanticroadgermany.com

Dinkelsbuhl is a town about the size of Rothenburg with the same late medieval architecture. However, without all the crowds.
Nördlingen is another medieval walled town built in a meteorite crater. The walls of the town are on the edge of the crater.
Augsburg is a city founded by the Romans under Caesar Augustus and worth spending a day.

"The walls of the town are on the edge of the crater." This sounds fascinating, indeed, but it isn't true. The crater has a diameter of 20-24 kms and the town of Nördlingen covers only a minor part of it. Besides Nördlingen there are several little towns and villages inside the crater. On nice days you can see the rim of the crater from the top of Nördlingen's famous church tower, the so-called 'Langer Daniel' (Long Daniel). Geovagriffith, you shouldn't keep repeating this wrong piece of information.

Perhaps his confusion arises because the actual city walls, as well as many of the houses, were built from rocks quarried from the crater wall.

The impact also created suevite —an impact breccia or course-grained rock comprised
of angular fragments that can include glass, crystal and diamonds,

The crater walls would make lousy town walls as the crater wall is not continuous; there are enormous gaps.

I also disagree on the idea of renting a car and driving the Romantic Road. The Romantic Road, as a road, is over-hyped. The road itself is just an ordinary German country road, two lanes, winding, choked in summer with tour buses, lorries, and farm equipment. The Road is not that special - it's the towns along the road. Most important towns, except for Dinkelsbühl are accessible by rail.