Unfortunately the only place in Nicaragua I've surfed is San Juan del Sur, right across the border from Costa. When it's firing, it's the place to be. When it's not firing, it's still good. Great, laid back atmosphere as that's where a lot of the gringos in Costa go to renew their passport. And you're close to good surf in Northern CR. I've heard great things about further up in Nicaragua, a lot of which is still trying to be held secret. Get the The Surfer's Guide to Costa Rica, the "bible" equivalent of the area.
Utilize the bus system and don't call a Nico a Tico.