I did click on your link, but all that came up were a bunch of little blue boxes with question marks.

I have little experience in desert or jungle hiking and none at all in Mexico, so I can't really be of much help there.

I do have considerable experience horsepacking, though. First of all, the pack animal (horse, mule, burro, llama) has considerable requirements for itself. Your burro will need to carry its food and water and other gear (such as a picket line for night, an extra set or two of shoes, etc.), so its pack won't have much room for human gear. In addition, taking a pack animal is similar to having a young child along--a lot of extra work and time. Which is fine if that's what you want, but do be warned--the burro will slow you down!