Hello Martin,
You will have fun! Most people use Garmin GPS and Bicimaps software for Mexico. Probably not worth buying in your case since you will be in Mexico for such a short time. If you have hundreds of dollars to spend then okay, but I'm poor and found paper maps to be fine heading through Mex and Central America. (Thrifty is nifty). I use ITM (International Travel Maps) available at Barnes and Noble where you are and Guia Roji for Mex, available in Mexico. You will get hopelessly lost in the big cities at some point since there are no street signs. Imagine traveling through Atlanta with no street signs. I look at it as a game. You win if you make it several miles through the town of a million people without asking directions. You lose if you give up and hire a taxi for some pesos to lead you through town to the highway on the far side. Nothing beats weaving through town following a latino cabby. You get better at the game as time goes by. I can remember what a feeling of triumph it was making it through Acapulco unaided without a map. Of course if you head down the gulf side navigation is pretty easy. None of the maps are that accurate, and I hear GPS is sketchy in Honduras and Nica so everyone is asking directions alot.
Two weeks from Biloxi to Nicaragua doesn't leave a lot of time for flat tires and exploring though. But I guess you know that. Everybody and their mother will be telling you how dangerous your trip is. If we listened to those people just think of all the wonderful travel memories we would have missed out on.
Look forward to reading your travel stories.

Best luck,
John

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South America and back on a 250 Super Sherpa Minimalist Adventure http://advrider.com/forums/showthread.php?t=831076