I've read a few travelogs of people who've done that. It seems that you'll be taking lots and lots of buses, and their dependability and efficiency will leave lots to be desired. So, take a lot of patience and understanding.
Also, read a newspaper with good international coverage (NY Times, etc. -- not USA Today, or "McNews" as it's called in the business) regularly. Find out where the especially hot spots are, politically. Like Darfur in The Sudan...obviously, avoid those places.
Finally, you might look into the money situation. Talk to your bank and see if they have suggestions for setting up either an account with banks along your path in various capital cities or whatever (so you'll have access to cash), or if they can verify that your particular ATM service will be active there. The last thing you want to do is load up on cash and then get held up, and be out the money, and likely the trip.
Good luck, and keep us posted on things you find out. Sounds like a helluva adventure!
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"Life is not measured in the number of breaths we take, but by the places that take our breath away..."