Colors, Statistics.

How to change object colors? May be opacity to)?
Also is it any way to see how many triangles, quads and ngons are in scene?

You can use materials to change colours and transparency of objects and even individual polygons.
To display poly count statistics, turn on HUD in View->Display->Heads Up Display->Show Heads Up Display, then enable View->Display->Heads Up Display->Show Scene Info.

rubberDuck, but how to use those materials? Have no idea
Show Scene Info does not show amount of triangel, ngons etc.

Show Scene Info does not show amount of triangel, ngons etc.

As a workaround, you could use math selection to select those types of polygons and then take a look at the selection column in the heads up dsplay.

rubberDuck, but how to use those materials? Have no idea

Open View->Windows->Material Window. RMB-click on thumbnail opens a menu where you can create a new material or assign it to currently selected object for example. You edit material properties in the Texture and Colour groups. Diffuse Alpha changes material opacity (and thus - the opacity of objects that the material is assigned to), Diffuse controls diffuse colour, Ambient sets the colour of surface that is not directly lit, Emissive makes object "glow", Specular Sharpness and Strenght are self explanatory.

If you don't want to change an object's material, but you need to make it temporarily transparent, you can use View->Object Shading->Object Individual Shading->Transparent.

Thank you!