Until there is a separate forum (BTW I think this thread works) here is my key advice:
1) Rough out your minimum route with free planning software (ex. MapSource, BaseCamp. BaseCamp is the latest and greatest from Garmin. I recently switched over and am happy with it.) Route reasonably sized segments, one or two days long, not one long route. Making one long route doesn't work well when uploaded to a GPS and you make a small change while riding, which forces the device will recalculate the WHOLE route.
2) Add up the miles, then calculate minimum amount of fuel, tires, oil changes, and estimate the cost
3) Count number of days planned to stay in one place and ~400 miles highway or ~200 miles dirt per day (very subjective) to estimate hotel nights, meals and in-country insurance.
4) Estimate border fees...too many variables to comment here.
Understanding the above is important if traveling through malaria prone regions and getting the right count of anti-malaria pills (don't try to get them on the road...)
Cross check: look at the total number of miles and divide by the number of days you are planning. Does the number of miles per day sound reasonable? It should be a smallish number, due to days spent not traveling and lost time crossing borders.
Hope you find something useful in the above.
NYC to Tierra del Fuego (and back!) 2012/2013
Blogs: Peter's Ride