I've shot weddings in Germany and Scotland before, no Mexico but each do require a work permit. I can't really comment and don't want to give you bad advice regarding obtaining a work VISA but here are a few things you may want to consider regarding gear and traveling.
1. Always have your camera equipment as carry on luggage. I have a Pelican 1510 that is the exact dimensions for carry on.
2. Declare your camera equipment with US Customs, especially when you bring a lot of equipment and traveling to country with a lower currency exchange rate like Mexico. I use form 4457 to declare all my camera equipment so I don't get hassled when I bring them back. The US Customs office will have to verify and sign it off before you leave.
3. Have international insurance coverage for your equipment. Most business insurance do not cover internationally by default so you have to verify that with your insurance company.
4. Book your own itinerary and bill it to the clients. The clients will always go with cheapest route, not the most practical.
5. Make sure to have the correct power plug/adapter for your electronic equipment. I have a small power strip so I just use 1 adapter for all of my devices.
6. Give yourself some extra time after the wedding to travel and site seeing if that's your thing.
