Thanks to everyone who posts on the forum, answers questions, and shares experience! Maybe someone in the future can benefit from my report. :)
We divided our trip into the following: 1 night Cordoba; 4 nights Seville; 3 nights Granada; 1 night Madrid before a morning return flight.
We arrived via a connecting Lufthansa flight from Frankfurt in Terminal 2 at 3:30. I had pre-purchased Ave tickets from Atocha to Cordoba for 7:30, so we used the airport shuttle bus to T4 to use our free Cercanius ticket from the airport. It was a bit of a “winding route” to the shuttle but it was well-signed and an easy process to find both the bus and the Renfe line. At the ticket machines, there was an agent helping everyone retrieve their free ticket. For those new to the process, you insert your ticket into the slot and it pops up on the top of the turnstile just in front of where you put it in but before you go through. Then the turnstile opens for you. Keep your ticket - you repeat the process to exit once you get to Atocha. We ended up with a long wait - could have easily caught the 6:30 train but I wanted to be sure we had a “sure thing” in hand.
Once in Cordoba, we caught a taxi (€7) to our Airbnb a stone’s throw from the Mezquita. After getting settled, we wandered the perimeter of the Mezquita and by the river. Truly beautiful at night! Our host had provided coffee making supplies, so the next morning after feeding our addiction, we headed to the Mezquita when it opened at 9:30 (a Sunday - this meant it wasn't free during the morning hours but didn't have a choice on that). We were some of the first people in and we really didn't encounter any crowds. An hour and a half was sufficient for us. We then spent some time walking through the Jewish quarter (spent a few minutes in the synagogue) and the old city walls. We ended up back by the river and walked across the Roman bridge and down by the water on both sides. By then we were ready for lunch so we enjoyed a long leisurely “menu del dia” at**. Then it was time to grab our luggage and taxi (€6) back to the station for our 5:44 train to Seville. (Our host had graciously allowed us the extra few hours).
Seville was just lovely. Again we stayed 4 nights in an apartment a stone's throw from the Cathedral. Here, more than anywhere, we followed the wisdom of someone on the board who said “You can't do it all, so enjoy what you see and do, with no regrets.” Toured the Palace and gardens and the Cathedral, did not manage to climb the Bell Tower, explored the Santa Cruz neighborhood, wandered through Triana and the market, walked and sat by the river, visited Plaza de Espana twice, and ate lots of tapas. My daughter also rented a bike for an hour in the gardens near Plaza de Espana and experienced some grassroots flamenco (not the kind where you attend a show), and climbed the Torre del Oro (free on Monday). Seville was a marvelous place to “be”.