Model orientation and size?

Two questions:

When modelling for source using Blender, how do I set the size of the model?

Also, is it possible to choose where a model spawns in relation to the prop entity? For instance, if I wanted to replace a prop_physics in Half-Life 2, would there be a way for me to always make it spawn just above the floor, even if the new one’s bigger?

I hope this was comprehendable.