Modeling for Unity 3D?

I am very new to Unity 3D. Before i start making models for my game, i want to know how big i should make objects? How do i get a model to reference: Like a character?

I have had some scaling issues, with animations, the Physics of the model etc. How do i start? Thanks!

The Unity standard scale is generally referred to as 1 game unit = 1 meter. So if you place the default primitive cube in a scene, consider that to be 1 meter tall, thus a fairly tall characterPlayer might be 2 cubes tall.