First, these forums are primarily for the support of user-contribed GPSFileDepot maps and not Garmin products/software. I would suggest this site if you want to discuss the Nuvi (I'm a moderator there):
http://forums.gpsreview.net/categories/garmin-auto-forum-garmin-nuvi-forumBut here are a few thoughts. A 32gb card is overkill for the Nuvi, you should never need anything near that size, although it should work. Maps installed on the card must either be in a folder named Garmin or Map. When the Nuvi starts, it will check these locations for any files with an .img extension.
Waypoints (favorites) and routes are .gpx files. You can place them either on the card or in internal storage and they will be read/imported when the device starts. The device will always save user data to internal memory however and not the card. All your routes, favorites and tracks will be in the file named Current.gpx that is found in the GPX directory in internal storage.
That file is just a copy of data that is stored in protected memory on the device and cannot be directly accessed. Whenever the nuvi starts, it dumps all your data to Current.gpx so that you can access it. But that file is not actually used for anything by the Nuvi, and you can delete it without causing any problems.
If you use Garmin's own software for map updates (Garmin Express) it will automatically choose the place to put the map. I have not used this very much, and it is confusing. If you want to discuss this, use the gpsreview link I posted above, there are people on that site who should be able to answer you specific questions.
Routes and favorites are very small files, you should not need a card for these, they take up almost no space. The map itself is the only thing that needs a lot of space (about 3gb).