Yes, you will need a passport to travel to Mexico. Please note, getting a passport for the first time can take up to 6 months. Remember to check your passport expiration date! Please visit this website to find out more about applying for a passport as an adult: https://travel.state.gov/content/travel/en/passports/need-passport/apply-in-person.html
You do not need to speak Spanish as most people in Mexico City speak English. If you would like to learn, bookmark this link for common phrases in Spanish! https://blog.rosettastone.com/102-essential-spanish-phrases-for-traveling/
Please check this link for the latest conversion rate as it fluctuates: https://www.google.com/finance/quote/USD-MXN?sa=X&ved=2ahUKEwjulJTP6e2JAxVtFlkFHWx2FlYQmY0JegQIIhAu
You do not need cash to get around in Mexico City as most places take card, but please note that tax in CDMX is 16%, so if you can get pesos when you get there, you can sometimes avoid the high tax ;)
We will arrange transportation for the wedding events. If you want to explore alone, we recommend Uber.
If your invitation/save the date has a +1 or says "and Guest," you may bring a date.
We will have 2 hotel blocks, where transportation will be provided to and from the wedding events (check back in July.) If you would like to stay elsewhere, Mexico City has many great options with AirBNB and other types of accommodation, but please plan to arrange your own transportation or walk to hotel pickup for the wedding events.