It's not crazy. It's a beautiful route and there's no reason not to walk it the direction you want to walk. I think the Camino is a lot about making choices, deliberately. So do it if you want. The route is a bit up and down, but worth it for the vistas. Plus the Basque country is a very special place to visit.
Have you seen this site?
http://www.consorciobertiz.org/menu-cen ... anguage=en
and this page describes each stage of the Baztan route:
http://www.consorciobertiz.org/menu-cen ... ation.html
Also this site:
http://www.rutasnavarra.com
which is a bit complicated but if you select Camino on the right hand menu, it will give you a map and you can find the routes for the Baztan route and for instance here is the stage 3, and it shows the route on the top map but below you'll see the elevation:
http://www.rutasnavarra.com/Rutas/Camin ... 10013.html
I did part of this route in May of last year, from Urdax to Pamplona. The markings aren't as clear as other places on the Camino, and it was absolutely the route less traveled (I saw no other pilgrims) but it was stunning. You won't find refugios and albergues as easily as on the
Camino Frances, though, so thinking ahead about accommodation is probably necessary. The first link I gave you has recommendations.
I will make a recommendation, too. In Urdax, just off the trail, is a lovely Casa Rural (B&B) that is one of my favorite places on earth:
http://www.irigoienea.com so if you pass by you might want to spend a night here and I think you won't regret it. Also in Urdax, a fantastic paella can be found at the restaurant Koska.