Frida's Caza Azul is best done by prior booking online to guarantee your entry time. When i was there with a tour in January, there were no waiting lines for entry, only with prior booking. People who turned up were told to go and book for another time as those were the new rules. To get there, it is not necessary to take a guided tour. You can take a taxi/ Uber there, just ask for Coyoacan & Casa Azul.

The pyramids are well worth a trip. There are lots of buses, but i would hire a guide (there are some there on site, or take a tour). There is so much info that you do benefit more from a guide at a site like this. And just an fyi, you can no longer climb either the pyramid of the sun, or the moon. After covid they kept them closed to stop wear and tear, same as at many other sites now.

Definitely visit the National museum of Anthropology in Chapultepec park, you can easily lose a day there exploring the museum, plus there are a ton of other galleries and museums nearby with low cost entry fees.

On the Zocalo there is the Metropolitan Cathedral, Templo Mayor (Aztec capital ruins and museum) and the departure point for the Touribus - the open top sight seeing bus. The cost of the bus is around $200 pesos per person and well worth it.

Just behind the cathedral is a well known and clean and cheap hostal, I forget the name, something like Mundo Joven to look at.

If you want I can send you one of my tour itineraries if you send me an email and from that you can see the activities I do to give you an idea. Email - info @ flipflopnomads.com

Any other travel advice or ideas about the city i can also send you info and help you out if you want (free service fyi, i don't charge for stuff like that)