Optimizing Graphics Performance... 2D?

Hi everyone,

I have some questions regarding the documentation for 2D development in Unity. Some friends and I have been working on a concept for quite some time now. We're planning to develop an RPG game for tablets and phones. For some months we have been designing the story, characters and basically done nothing but narrative design.
We're starting to get to a point where we have to pin a style, create concept art, design the mechanics and start making some prototypes.

The one thing we know is that we want the game to mostly be 2D. We're still doing some research on whether or not it is more effective to have 2D sprites for characters, or 3D characters. I've been told that 2D games mostly requires RAM, whereas 3D would also need CPU power. Mixing it up seems like an alright balance.

Unity thus far seems like the perfect engine, we have been looking at this engine ever since the 2D support came out. We are currently working with designers and artists, but not any programmers. We don't have that much experience with developing 2D games, not in a serious matter like this project anyways.

I really like the way Unity has its documentation, there is plenty of information to find except for things like how to optimize our graphic performance, 2D wise. Since we don't have the experience and knowledge I was hoping that these documents do exists, and that somebody can link me to them. Or perhaps somebody knows if they have yet to come.

If that isn't the case, then I'm looking for as much tips & info for developing 2D games in unity. In order for us to create a style and make some prototypes we would really need to know what our limit would be in everything.

Let me know where to find these documents, or if you have any information / experience yourself please share!

Thanks