September trip to Andalucia

I personally would take a day or two from Cordoba and add it/them to Sevilla or Madrid.

I also wonder to reduce Cordoba. I did spend 2 nights but as coming from Seville by train, had the better part of 2 full days. If you want to add the Roman ruins outside of town, then maybe a 3rd night. I saw a lot the Old town had to offer including their archeological museum, and still had time to birdwatching from the bridge and wander the far side. (But was 7 years younger than now).
I tended to use the train, but I did buy my ALSA bus tickets on line a few weeks before departure. I don't think they their price shifts much. They seem to just add another bus when one is full. I bought them directly from the ALSA website, but my Canadian credit card rarely has issues with European online purchases. YMMV.

I LOVE the pace of your itinerary!
You shall have ample opportunity to create wonderful memories of being there in addition to seeing there.
If you are amenable to sitting in second class coach, which is n excellent experience and the one we purchase, I believe you do not need to make advance purchases. Following this suggestion provides addition flexibility to mending your travel s you may desire.
Enjoy!

I don't want to discourage 4 nights in Cordoba, per se, because it has great wandering-around possibilities as well as quite a lot of sights, but you are short of time in Seville and Madrid, which are much larger. I, too, would shorten the Cordoba time just so you can manage Seville and Madrid more easily.

I agree with recommendations to take 2 nights from Cordoba. Add one night to Seville and one night to Madrid. We love Cordoba, but Seville is larger with more sites so you really need 4 nights in Seville. And Madrid deserves at least 3 nights, too. Otherwise, you have an awesome itinerary.

In Seville, for sightseeing, I also recommend Casa di Pilatos. Plaza de Espagna is gorgeous! Visit the Triana neighborhood including the Mercado. Take a carriage ride. Seville is gorgeous.

In Cordoba, also visit the Alcazar and Palacio de Viana.

Thank you all for your responses. I am still leaning on a longer stay in Cordoba because the history and architecture of the city looks so fascinating. I will happily look out over the Mezquita every night we are there. I know our days in Madrid are very limited but am hoping for a future trip to Spain to include both Barcelona and Madrid and some of the cities in the North. I originally intended to skip Madrid but it didn’t make sense to have 2-3 layovers on our flight home. We will make the most of our time there.

I would have no qualms about giving Madrid short shrift, if only because you are very likely to come through Madrid the next time you are in Spain. I'd consider giving it one night so you could add a day to Sevilla.
Not that is really matters at all, but I liked Cordoba better than Sevilla!

For me, taking a day or two from Cordoba and adding it to Sevilla or Madrid is less about which city is more likable and more about the relative size of cities and the respective number of things to see.