Spain on our Own

3 places to stay for a month sounds about right. The Northwest area has a lot to offer also
https://www.tripsavvy.com/northwest-spain-guide-1643970

I guess it would depend on where the rental homes were and which places you planned on taking day trips to. Many of the major cities are not really conducive for day tripping between without a lot of travel time. Day tripping to smaller of mid-sized cities might be easier to plan. Without knowing which you planned on using as home bases, it’s not easy to answer the question. To adequately see Spain, one must make multiple trips to it and concentrate on smaller areas or regions at a time.

I don't know how you define "major cities", but one could easily spend more than a week in Barcelona, and you wouldn't want to pay for a rental car or parking while you were doing so. It really wouldn't make sense to stay in a small town and make repeated trips to Barcelona because you'd be paying for train tickets or parking over and over again as well as wasting a lot of time.

The same would be true for Madrid if you have an interest in art. If you're not big on art, I guess you might get by with just a day or two in the city itself.

Seville is worth multiple days. Granada probably needs two so you can devote most of one to the Alhambra and another to the rest of the city.

You really need to come up with a list of towns/cities you want to see and some idea of how many days you'll want in each one, then consider the best mode of transportation. Fast trains will get you from Barcelona to Madrid to Cordoba to Seville much, much faster than you can drive. Some side-trips are so easy to do by train (Girona, Figueres, Toledo, Segovia) that you don't benefit from having a car when visiting them.

As you've noted, Spain is large, and the hub-and-spoke-by-car method of travel is going to have you spending a lot of time in a car. I really don't think it's a good approach in most parts of Spain.

Areas where a car is very handy are the Basque Country, Galicia (in fact a car helps all across the north, though it's not 100% essential), the Pyrenees, and the white villages down in Andalucía. But how many miles are you willing to drive out and back each day??

What time of year is your trip? If you're planning for next summer, research historical weather conditions in the south before committing to including Andalucía. The average monthly high temperatures (not the record highs, the average highs) in Seville are 100F in July and August.

... contrary to other "territories", this is a piece of land with plenty of things to see "between cities", so regardless of "how far" the distance between them is, you'll find many places worth exploring.

No problem finding great places to see, but you might miss a place you'd rank in your Top 5. I'm thinking specifically about Granada. Unless you choose to have two of your three bases down in Andalucía, I think you have a choice between seeing Seville and seeing Granada. Some folks seem to have a hard time saying, "We'll get there next time"; others are fine with picking a limited area and seeing some charming, less-touristy spots as well as just some of the Big Name places.

I fall in the second category myself, but it's my impression that I'm in the minority.

Right there with you acraven. I’m all for those smaller less-touristy places. A lot of great places to see and visit are off the beaten path.

Fairly large?

I just learned of this fun resource that shows a size comparison between various countries and/or states and other countries and/or states. Fill in the boxes and be amazed.

For basic info on how far it is, how long it will take and different ways to get there, use Rome2rio.

I have found that Rome2Rio is all too often quite inaccurate about bus/train fares, travel times and frequencies. It's pretty good about the actual existence of buses and trains, and the places where you might need to transfer. For the nitty-gritty details about schedules and costs, I think you really need to keep drilling down until you find a link to the company that operates the train or bus you're interested in.

Agreed! But it is a way to get some simple comparisons and to see some maps for each option.

I'll grant you the maps, but I'm afraid of the comparisons because I've seen some really wild data showing up.

I've spent about 7 weeks in Andalucia on 3 trips in the past 5 years. Sevilla is the only place I would consider using as a base. There are plenty of sights in the city itself, Cordoba, Jerez and Cadiz are reasonable day trips by train and you can even see Arcos by taking the train to Jerez and then a bus to Arcos. I'd rather spend 2-3 nights in each place. Sevilla 3-4N, Cordoba 2-3N, Jerez 3N (and day trip to Cadiz and Arcos).

I guess Malaga could be a base for the south, with Granada as a long day trip, but it's a 2-hour bus trip and then you still have to get to/from the bus stations in both cities so figure between 5 and 6 hours travel time. With a car, it would be less of course, but parking in Granada could be a hassle, driving in the city certainly is. You could explore the Costa del Sol (not that interesting to me) or some of the hill towns, but that's hours of driving also.

There's plenty to see and do in Barcelona, add in day trips and you could fill 10 days without a problem.