Ratty - From what I'm seeing with Unity's Mecanim system, you make animation clips in your modeling program of choice (Blender in this case) and Mecanim provides a state machine to blend animations together and create 'in-between' animations like running left/right, etc...
That's an excellent question on gravity. I will have to see.
As for poly limits, I'm nowhere near hitting anything unacceptable. I just really like lower-poly models. They give more of a 'game' feel in my opinion.
Kat - I haven't been stressing too much on detail because of the fact the character will be far from the camera, however, in the future, I'll be doing a very similar game with a perspective camera which will be able to zoom in up close on the model. Eventually I'll end up modeling eyes and such for eye tracking and whatnot.
Currently the face uses a 128x128 diffuse, the body will probably get a 256x256 since there isn't going to be too much small detail. I might stop living in 1998 and use a 1024x1024 for the body and 512x512 for the face.