This is definitely doable, but it wouldn’t be my choice.

I think the concept of saving money by taking overnight trains is overrated. A berth in a 6 berth couchette costs 20 to 30 euros — roughly the same as a bunk in a hostel dorm, so not a great money saver. A berth in a 4 berth couchette (closer, but still not comparable to a hostel dorm in terms of comfort) costs 30 to 40 euros. Seats aren’t even available on many overnight trains and when they are available they can cost up to 15 euros, so even if you manage to find a few trains that have seats, it won’t result in huge savings for your trip.

I don’t care for overnight trains, so I would not enjoy taking an overnight train every 4 or 5 days. My rule of thumb is 1 overnight train per week, so maybe 1/2 what you’ve planned. My 6’1” husband and 6’2” son like them even less. Their rule of thumb would be: Only when there’s no other way to reasonably accomplish the trip….

Check your library for a copy of Europe by Eurail or see if you can find a cheap used copy of an older edition. It uses the “base city/day trips” style of travel that you’ve described. I don’t consider it a great general guidebook as it’s not very detailed and has no city maps, or specific information about attractions, but it’s great for a general “how to do it” description of this travel style.

Second that on the overnight trains, you’ll ruin your trip by constantly being tired.

Four days in Madrid, you’ll be bored after day 2 I’d say.

We just got back from two weeks in Madrid. It was very interesting, other than the pickpocket that got my wallet. They warn you about them, but they are very deft, so be careful.

They have high speed trains to Toledo and Segovia, which cost about 20 euro round trip and make a nice day trip.

And if you like art, they have a wealth of museums, with the Prado, one of the great museums of the world, the most noted. There is more in the Prado alone than you could see in two days.

I agree about the overnight trains. You don’t see much scenery at night (one reason I like train travel) and many of them have layovers and train changes that can interfere with your sleep and make the trip longer.

I spent 4 days in Madrid and wasn’t bored at all. The Prado was fine, but I preferred the Reina Sofia- spent nearly 4 hours there, and could have spent many more. Siesta in the afternoon in Retiro Park. Toledo was a great day trip, but you’ll save a ton of money by taking the bus rather than the train. It’s still less than an hour by bus, so totally doable as a day trip.