Well, I wrote about how to prepare an RTW-trip before, starting in New Zealand and had a site each for the countries I visited, but all these countries I visited during part 1 of my RTW-trip were English-speaking countries. That can be important if you are a good English speaker, but does not have any knowledge about roman languages like Spanish. Even I know some Spanish, I feel it is not enough for my travel, though I decided to make a month-long homestay as a helpx-helper and improve my Spanish at that time.
There are more differences. There was not a high risk at all to get some health problems in the countries I have been so far. For Mexico and the other Latin American countries you have to be more careful and you have to prepare in time, because there are lots of vaccinations you should take and also, if you are older than 30 years, you should remake your vaccinations you have got as a child, which are: Diphtheria, whooping-cough (pertussis), tetanus and polio.
In addition to that it is recommended to have the following vaccinations for Latin America (I use the expression “Latin America”, because all the countries from Mexico in the North to Fire Land in the South are included, meanwhile Mexico also counts to North America (therefore you find it here) and there are countries I will visit this time in Central America as well):
Hepatite A+B, typhoid fever, cholera. All of these vaccinations you have to take more than once within special timeframes. Furthermore you need the vaccination against yellow fever. There are countries, which won’t let you enter without this vaccination. Luckily you only have to take it once and it gives a life long protection.
There also are two more life-threatening disease, you can get in those countries: Malaria and Dengue fever. For both of them there are no vaccinations yet. The best protection against the mosquitoes, which spread the diseases, are clothing (long sleeves and long legs during evenings and nights) and bed-nets impregnated with insecticides while sleeping as well as repellents during daytime. Read more about how to prevent Malaria by the link. You also can take Malaria tablets during and some days after the time you are in a “Malaria area”, but you have to know, that there are different kinds of mosquitoes, some of them are immune against the usual medicine and you need to take another kind of it (it is similar to the penicillin). Therefore, the best is to look for this medicine at your destination, because the doctors there know, which one of them will be effective in just that area. See also the site of the WHO and their information for travellers. For the dengue fever you only can protect yourself against the mosquitoes.
Pay attention to, that there are no many people, who get sick in Malaria in Mexico and the Central American countries anymore, but it is different from country to country and in Mexico it depends on the state, where you are. UPDATE (Jan 2019): The doctors in Mexico told me, that there is no risk anymore for Malaria in Mexico. There are maps about it to find on the Internet as well and also country profiles – they open as a PDF! The highest risk is still at the country side of Guatemala, but there are also only a few cases each year.
Though with all I wrote about Malaria and Dengue fever, you have to create your packlist. My decision was to buy some new clothes in Mexico. The Mexicans should know how to protect.
Don’t forget your usual medicine and the first aid kit!
Last but not least the visa. As an European citizen (Schengen) you do not need a visa for Mexico if you are registered in an EU country. On an official site about visas for Mexico you can choose your country and check, if you need a visa. At the border, you will get a document for the time of stay you ask for. When I was in Tijuana in 2016 e.g. I asked for 3 days only and it was written in the special field 3/180. Why 180? The maximal time you may visit Mexico in a row (as a tourist or even business traveller) are 180 days, but it is common, that you can leave the country just for a couple of days or a week maybe and go back and get one more time 180 days. By the way it does not matter if you are coming by flight, boat, car or walking.