Use multires modifier to lower the polygon count.

(Apply the modifier, hit the generate button, then set a percentage to reduce it by)

Multires works better than the optimise modifier in this case because multires maintains your UV information and the textures wont go all crazy.

Scaling the model should be as simple as using the scale tool right click the scale tool icon and punch in a number or scale in the viewport. If you still have issues with the model you may need to "reset the transform"

You do this by going to Utilities>reset X-form>reset selected. This copies the transform data ie: The move,scale and rotate data into an x-form modifier. collapse the stack afterward. That should usually avoid weird issues.
If you need your object to be a specific scale you need to set your system and max units to something like centimeters then create a box, or something with a specific hieght and width. then scale your object to match the box.
Hope that helps...

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