Hola Roberto .
Is it a one way trip or are you riding back also? That would make a difference in logically setting up some points to visit in a neat sequence
Consider these ideas as part of your route to Panama

South in high country through OAXACA, and all the way through on the Pan Americana , the usual sights in Chiapas san Cristobal and the mountains of Guatemala- Lago de Atitlan, Panajachel, Solola, Chichicastenango , Antigua
Then into Honduras to Copan ,
Into Costa Rica many possible routes but recommend at least the ride around Lago Arenal and volcano views , other volcanos to ride up around Central Valley and the road south to San Isidro over the mountain tops

If you have a round trip planned maybe go to Palenque , then over to the coast at Chetumal and do a bit of Belize then, enter Guatemala for the closest entry to visit Tikal , Fom there either go south via Coban or Rio Dulce
and into Honduras via Corinto to San Pedro Sula and from there it would need to be back southeast through Tegucigalpa and to Nicaragua

Panama could be entered at the north coast at Sixaola CR or at the south side of the country both every interesting .
The point is that there are so many possible ways to go and it is only a case of deciding. Have fun is the main goal and you will find plenty to keep you interested as to discover stuff along the way without planning

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93