Train pass vs individual tickets

Using DB app is meaningful for single tickets because it informs you also about changes or delays.
When booking single tickets you shall book asap, may be Flex tariff if time window is not sure.

Do you travel alone?

Spouse and I are traveling together.

Heidelberg to Ittlingen one day 55E roundtrip, 1 hour

€55 is too much, I think. This is a 47-min. direct train ride (one way) on the S-Bahn (a regional train) for which there's a day pass (the Baden-Württemberg ticket) which costs €33/2 persons. You could travel on regional trains around the entire state of Baden-Württemberg with this ticket on that same day. It certainly will cover that small round-trip journey. You can buy it at the station from a ticket machine or by app. Don't buy it in advance - there's no price advantage and it's non-refundable if your plan changes.

Map of B-W:
http://www.agilis.de/wp-content/uploads/2016/11/Streckenkarte-BW-2013.jpg

I'll be spending lots of time purchasing tickets and rushing to catch trains.

It's not clear to me why this one ticket would take a lot of time. No rushing either as long as you arrive a few minutes early for this trip.

Heidelberg to Rothenburg o.d.T. - 4 hours, 55E (2 days)

A round-trip on separate days will require separate tickets. I believe €55 might be the one-way "saver fare" price for two persons, correct? This destination is a small town at the end of a trunk railway in Bavaria and thus requires multiple changes of train if you start in Heidelberg. There's a 4-train sequence that takes about 3.7 hours leaving Heidelberg at 9:13. Is that the trip you are considering? No ticket or rail pass can change the multiple changes of train on this route. Buying the ticket doesn't take much time, just keep in mind that saver fares are either non-refundable or partially refundable and lock you into a travel schedule. DB does sell a refundable / schedule-flexible ticket (flexpreis) for this route, but it will cost you nearly €300 round trip for the two of you.

Perhaps Rothenburg just isn't the right trip for you. There are excellent old-world destinations much closer to Heidelberg, you know.

Bad Wimpfen, 70 minutes, one change of train, €33 round trip for two (B-W Ticket/daypass again,) pretty train ride along the Neckar River

Ladenburg and Heppenheim, 17 minutes and 37 minutes respectively by direct train, €22 round trip for two on a VRN "family" day ticket (buy at station,) both located on the "Bergstraße" wine route.

The German Rail Pass offers multiple days at high prices, mainly for people taking really long-distance journeys using high-speed trains. If interested, look into the flexi / twin-pass version:

https://int.bahn.de/en/offers/eurail

Thank you so much, Russ, for your detailed reply. The places chosen are due to family history. I know there are big distances between them. The only round trip is Ittlingen, from Heidelberg, as we will be based in Heidelberg for a few days and on one day will go to meet a genealogist. The prices I found were all one person, one way, on the DB site. Your prices sound better which tells me I have more research to do! my concern in buying the tickets is probably the planner in me thinking I won't understand the machines/how to buy the tickets in time to make the trains.

Note that tickets like the B-W Ticket are only valid after 9 am weekdays, but anytime on weekends.

You can also use a Quer durch Lands ticket to go from Heidelberg to Rothenburg and back to Frankfurt for 51 EUR per day for 2 adults. Like the B-W Ticket, only regional trains (no ICE or IC trains) and only after 9 am weekdays, anytime weekends. Using only regional trains adds about 30 minutes to the travel times. The QdL ticket is for travel across multiple German states.

If you want to go deep in the weeds, there is something called the Deutschland Ticket that is 49 EUR per person and valid for a calendar month for regional trains, buses, local transit. It is only available on a subscription basis, so you have to cancel it or it automatically renews every month. From Deutsche Bahn it requires a German bank account, but you can get it with a credit card through certain channels, like the Bremen Transit Authority (VBN). To say the least, its complicated.

Thank you, Sam. More research for me to do!

Deutschland ticket isn’t that tough to do if you are a person that is comfortable with doing things online.
I purchased mine through the MVV app one day for September and cancelled the subscription the next so I wouldn’t be charged for October. The key is to keep the email they send you confirming your purchase because it contains the link for cancellation.

Good suggestion from Sam to look into the QdL ticket for Heidelberg > Rothenburg. You can do the same for Rothenburg > Frankfurt.

Your prices sound better which tells me I have more research to do! my
concern in buying the tickets is probably the planner in me thinking I
won't understand the machines/how to buy the tickets in time to make
the trains.

• When you search for a journey, click on "only local transport" - this will pull up REGIONAL trains only and hide any high-speed trains. It is only the regional train journeys that are covered by the B-W Ticket, the QdL ticket Sam mentions, and the Deutschland-ticket Carol mentions.

• I understand your concern about ticket machines. So, try this... on the evening BEFORE your travel day... go to the station after most people are already at home, find an empty ticket machine, and take your sweet time there purchasing your ticket for the next morning. By that time, you should be pretty sure about your plans, right? Of course, you MUST be sure to specify the next morning's date, as you can't travel on an outdated ticket.