Ha, this is traditionally a Visual Arts forum question, but it's relevant here too.
I think you're getting a little ahead of yourself if you haven't programmed before. There's going to be a few Pongs and Tetrises before you can really consider making a 2D RPG of any scale. That being said, I would lean towards 2D since that's going to be easier to programmer art IMO rather than learning to sculpt, texture, and rig 3D models (although you might get a huge side benefit later on from learning that).
If I were you, I would keep a designer's notebook for your "Ultimate Project" but not really plan on implementing it as a whole until much later, like your 3rd year. If you're really passionate about this game, I would try to work on projects that prototype specific features, like a 2D tile game with only the most basic gameplay to get a feel for tilesets and maps, for example.
Basically, sit on your grandest ideas until you know you can implement basic ones. It's always much harder than it sounds to get even the simplest thing running, and running well.