The center of Oaxaca de Juárez (official name of the city) is small and easy to navigate on foot.
We put together this Google Map List with all the important spots: the ceremony at Grana hacienda, La Fabrica for the reception, and a handful of fav restaurants and mezcalerías.
If you're staying in the center — i.e. the area north of the Zocalo (main town square) — you really can get everywhere for the wedding on foot very easily. Everything is w/in just a few blocks. (But definitely recommend an afternoon wander south of the Zocalo to the market, etc!)
Don't forget to check the weather forecast before you leave. Should be mid-70s daytime / low 60s at night for late October, with occasional short scattered showers.
If you want to venture further out (highly recommended) to one of the mezcal distilleries or the ruins at Monte Alban or the mineral pools at Hierve el Agua, Taxis are also everywhere. You can just flag them from the street outside the pedestrian area (cash only). If you prefer an app, you can use Didi — an app like Uber that (usually) accepts credit cards — for rides around town or back to the airport. You can also obviously line something up through your hotel or one of the many travel spots around town.
There's a centralized system for taxis at the airport. After you land, just look for the airport taxi kiosk (pictured below 👇🏼) right as you exit security. You can buy a ticket for about 450–500 pesos (~$25 USD). They speak English, and you can use a credit card.
On that note, almost all restaurants etc in the center of town accept credit cards. That said, it's definitely good practice to get some pesos from an ATM before you leave the airport terminal. (Taxis in town prefer cash, as do a lot of the artisan / craft shops.) There are also lots of ATMs in town.